烟晶 Smoky quartz
烟晶 Smoky quartz
烟晶（又称烟水晶，茶晶或茶水晶）是一种固溶胶，属于胶体，以色均、无绵、明净者为佳品。在我国烟黄色、褐色水晶亦称为茶晶；黑色水晶则称为墨晶。烟晶的颜色是由于含有极微量放射性元素（镭）所引起的。实验中，白水晶通过放射性照射，的确可以得到烟晶。烟晶发源地在苏格兰，那里的人们广泛用它来装饰五彩缤纷的民族服装，成为事实上的“国石”。【烟晶 - 功效】促进再生能力的发达，使伤口愈合更快，增进免疫力，活化细胞，恢复青春，有返老还童的功效。能助事务分析及掌握能力，助品味的提升。尤其是吸收浊气，避邪效果最佳。强化海底轮, 所以对男性的性功能有显著的增强效果;对女性来说，也可调解血气，对妇女病有强化疗效的功能。 由于烟晶具有特别强的超声波，所以磁场强大，它的能量是向下发射的，烟晶可以防止某些灵修人士或用脑过度者，因下盘气场空虚而导致的阴气乘虚而入，弥补和增强下身磁场，加强人与地球磁场的连通能力，达到人体阴阳平衡。 烟晶的治疗能力非比寻常，它还可以使自私的人纠正歪行，治疗嗜烟、酗酒、药瘾及各种瘾症；舒缓精神分裂，对有自杀倾向，精神严重抑郁的患者很有帮助，可助消除恐惧及情绪波动，使人减少物欲而追求灵性的满足；也能治疗传染病及癌症。
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请选择举报类型！Smoky Quartz
| LinkedIn
Smoky quartz is a very protective and grounding stone. It brings physical and psychic protection. It is also an excellent stone for protection from negative energy, as It removes negativity and negative energy of any kind and transforms them to positive energy.Smoky quartz is beneficial mentally in several ways. It fosters cooperation in groups and supports their efforts energetically. It engenders creativity by bringing the same energies of grounding the creative process in reality to bring imaginative efforts to fulfillment & Smoky quartz also works energetically to assist in prioritizing needs and wants, and brings wisdom to every day life.Emotionally, smoky quartz is excellent for elevating moods, overcoming negative emotions, and relieving depression. Smoky quartz relieves stress, fear, jealousy, anger and other negative emotions by transforming them into positive energies. It is a helpful stone for enhancing and encouraging courage and inner strength. Smoky quartz is very comforting and calming, and can be considered a stone of serenity. It can, therefore, be very helpful in relieving grief.Looking for more of the latest headlines on LinkedIn?您好，欢迎回来
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16.55cts梨形瑞士蓝托帕石(swiss blue topaz)(13018)
16.55cts梨形瑞士蓝托帕石(swiss blue topaz)(13018)
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公司地址|广东 广州 番禺区 中国 广东 广州市 广州市番禺区沙头街银平路13~21号金信工业区1梯4楼
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材质托帕工艺打磨抛光加工定制否品牌srgems产品编号13018类别宝石裸石材料来源天然净度AAA形状梨摆挂形式挂饰包装PP袋独立包装尺寸20.00x14.50xh9.30mm
16.55cts梨形瑞士蓝托帕石(swiss blue topaz)(13018)
瑞士蓝托帕石(swiss blue topaz)，重16.55克拉,尺寸约为20.00x14.50mm,厚度9.30mm,采用中国千禧工(Concave Cutting)刻工，由升日宝石加工厂(Sunrising Gems&Jewellery Factory)依据原石的天然形状精心打磨而成，是制作个性镶嵌首饰及收藏，馈赠亲友等的理想选择。(www.srgems.com.cn)&&&&&&&&&&& 升日宝石加工厂隶属于升日国际实业有限公司,是一家以生产和批发天然彩宝戒面、彩宝首饰为主的专业工贸型生产企业；为番禺宝玉石协会会员，亚洲珠宝网站成员。公司于1998年创业至今积累了丰富的天然彩宝切割经验，同时拥有稳定的原料供应渠道，是国内彩宝的先行者及具有一定实力的供应商。从2004年开始，公司每年定期参加广州，深圳及香港国际珠宝展览会，在海内外拥有很高的声誉！公司竞争优势的产品是蓝黄玉（blue topaz）系列及各色天然彩色晶石系列！主要经营的产品品种有：一、各类天然彩色宝石戒面：*天空蓝黄玉(top sky blue topaz),瑞士蓝黄玉（swiss blue topaz）,伦敦蓝黄玉（london blue topaz），香槟黄玉（champagne topaz）,电镀黄玉(mystic topaz),白黄玉（white topaz）系列*各色天然彩色晶石:紫晶（amethyst）,黄晶(citrine),绿紫晶(green amethyst),粉紫晶(rose amethyst),粉晶(rose quartz)，威士忌水晶(whisky quartz)，金绿柠檬晶(golden green lemon quartz)，柠檬晶(lemon quartz)，茶晶(smokey quartz)，白水晶(white quartz)等*橄榄石（peridot）,海蓝宝石(aquamarine)*石榴石(garnet)，绿松石(turquoise)*其他各类宝石、玉髓等戒面二、各类镶彩宝首饰(color gemstone jewellery)；三、其他宝玉石雕件及工艺品；拥有多名专业技术工人，可进行各种形状的切割及设计，满足客户多方面的需求也是我们的竞争优势之一，我们可切割如下形状的彩宝：*各种普通切工*千禧工*双格子面，单格子面*吊胆*晶石配模和杂石配模*按客户的图纸及样品要求设计加工我们长期奉行“诚信，专业，双赢”的经营理念，坚持“品质优先，控制成本，交货及时，服务至上“的经营方针，朝着“更高，更专，更强“的目标，不断积极进取，竭诚为顾客创造价值！欢迎海内外客商及彩宝爱好者参观访问我们工厂！&
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升日宝石加工厂隶属于升日(香港)国际实业有限公司,是一家以生产和批发天然彩宝戒面、彩宝工艺品、彩宝首饰等为主的专业工贸型生产企业；为番禺宝玉石协会会员、亚洲珠宝网站成员、香港贸发局珠宝网站成员；是日本IJT珠宝展，美国TUCSON珠宝展，泰国珠宝展，印度珠宝展等国际珠宝展会的常年特邀贵宾。
&&公司于1998年创业至今师从德国和日本精湛的切割技师，积累了丰富的天然彩宝切割经验，同时拥有稳定的原料供应渠道，是国内彩宝的先行者及具有一定实力的供应商。从2004年开始，公司每年定期参加3月、6月、9月的香港国际珠宝展及不定期参加广州，深圳，北京珠宝展，在海内外拥有很高的声誉！
&公司竞争优势的产品是托帕石（又称黄玉，topaz）系列及各色天然彩色晶石系列！
&主要经营的产品品种有：
&一、各类天然彩色宝石戒面（裸石）：
&&*天空蓝托帕石(topskybluetopaz),瑞士蓝托帕石（swissbluetopaz）,伦敦蓝托帕石（londonbluetopaz），电镀托帕石(mystictopaz),白色托帕石（whitetopaz）系列
&&*各色天然彩色晶石:
&&紫晶（amethyst）,黄晶(citrine),绿紫晶(greenamethyst),粉紫晶(roseamethyst),粉晶(rosequartz)，威士忌水晶(whiskyquartz)，金绿柠檬晶(goldengreenlemonquartz)，柠檬晶(lemonquartz)，茶晶(smokeyquartz)，白水晶(whitequartz)等
&&*石榴石（garnet）,橄榄石（peridot）,海蓝宝石(aquamarine)等
&&*绿松石(turquoise),南红，其他各类宝石、玉髓等
二、各类镶彩宝首饰(colorgemstonejewellery)；
三、各类宝玉石雕件及工艺品系列；
&拥有多名专业技术工人，可进行各种形状的切割及设计，满足客户多方面的需求也是我们的竞争优势之一，我们可切割如下形状的彩宝：
&*各种普通切工
&*千禧工
&*双格子面，单格子面
&*吊胆
&*晶石配模和杂石配模
&*按客户的图纸及样品要求设计加工
&我们长期奉行“诚信，专业，双赢”的经营理念，坚持“品质优先，控制成本，交货及时，服务至上“的经营方针，朝着“更高，更专，更强“的目标，不断积极进取，竭诚为顾客创造价值！
&欢迎海内外客商及彩宝爱好者参观访问我们工厂！
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广东 广州 番禺区 中国 广东 广州市 广州市番禺区沙头街银平路13~21号金信工业区1梯4楼
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广东 广州 番禺区 中国 广东 广州市 广州市番禺区沙头街银平路13~21号金信工业区1梯4楼
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*联系我们时请说明来自中国供应商！Color smoky quartz and amethyst
Volume 9, pages
203-252, 1925
THE CAUSE OF COLOR IN SMOKY QUARTZ AND AMETHYST*& EDWARD F. HOLDEN,
University of
Michigan& ABSTRACT&&&&&
The nature of the pigments of smoky
quartz and amethyst was investigated from the standpoints of the occurrence and
genesis of those minerals, the effect of heat and of radiations upon the colors,
the transmission of light, and analysis for the various impurities. It is
concluded that amethyst owes its color to a ferric compound, while smoky quartz
is probably pigmented by free atomic silicon, liberated through the action of
radioactive substances. The literature is discussed as fully as space permits
and a chronological bibliography is appended.&&&&&
I. INTRODUCTION&&&&&
THE SCOPE OF THIS INVESTIGATION&&&&&
The causes of the colors of smoky quartz and amethyst have been the subject of
numerous investigations, in most of which only one or two methods of inquiry
have been pursued. But, any attempt to discover the nature of the pigment of a
dilute-colored mineral should be based upon as many different kinds of
experimental evidence as possible. The opinion arrived at by a single method of
investigation is not to be compared in plausibility to a conclusion substantiated by a number of converging lines of,
evidence. Therefore the research here described considered the following
principal subjects, all of which contribute their share to the final
conclusions:&&&&&
1. The occurrence and genesis of smoky quartz and amethyst.&&&&&
2. The influence of radiations upon their colors&&&&&
3. Color changes resulting from heat-treatment of these minerals.&&&&&
4. The transmission of light through amethyst and smoky quartz.&&&&&
5. The nature and amount of the impurities in these varieties of quartz.&A large
number of specimens were studied in order that some generalizations, applicable
to all occurrences of these minerals, might be made from the results obtained.&&&&&
The portion of the study devoted to impurities is almost wholly new. Those parts
dealing with the transmission of light, the effect of heat upon the colors, and
the occurrence and genesis are largely original. However, very little new work
on the effect of radiations was carried on, since that field has been very
thoroughly covered by other investigators.&&&&&
HYPOTHESES CONCERNING THE PIGMENTS OF SMOKY QUARTZ AND AMETHYST&&&&&
Various investigators have suggested that smoky quartz is colored in one or
another of the following manners:&&&&&
a) The pigment is an inorganic compound, probably of trivalent titanium. (15,
16).1&&&&&
b) The pigment is a carbon compound. (7, 9, 18, 19, 28).&&&&&
c) The pigment is a suspension produced by the action of radium radiations. (37,
The ideas which have been advanced as to the cause of the color of amethyst are
very similar, and may be classified as follows:&&&&&
a) The pigment is an inorganic compound.&&&&&
(1) It is a compound of iron. (2, 6, 11, 20, 22, 34, 56).&&&&&
(2) It is a compound of manganese. (28, 43).&&&&&
b) The pigment is a carbon compound. (18, 19).&&&&&
c) The color is due to the action of radium radiations. (41, 42).&&&&&
Each of the hypotheses as to the nature of the pigments is discussed in detail
in later portions of this paper.&&&&&
LOCALITIES AND DEPTHS OF COLOR OF THE SPECIMENS STUDIED&&&&&
The localities and the depths of color of the various specimens of smoky quartz
used in this investigation are given in Table I, below. The variation in color
is indicated by four color-classes. Class i includes the dark blackish brown
specimens, darker than Ridgway's2 13&m; class ii, smoky brown,
17''' 13&m; iii, pale grayish
brown, lighter than 17'''; and class iv, almost colorless. The order of
arrangement within the four classes is not intended to be significant.&&&&&
TABLE 1. LOCALITIES AND DEPTHS OF COLOR FOR SMOKY QUARTZ
Color-class
Specimen& number
Pike's Peak, Colorado
Pike's Peak, Colorado
Florissant, Colorado
Butt Township, Ontario
Conger Township, Parry Sound district, Ontario
McDonald Mine, Monteagle Township, Hastings County,
Mining Corporation Claim, Butt Township, Ontario
Lyndock Township, Renfrew County, Ontario
Seffernville, Lunenburg County, Nova Scotia
Auburn, Maine
Seneca Falls, New York
Alexander County, North Carolina
White Mountains, New Hampshire
Bedford, New York
Branchville, Connecticut
New Kingston, Pennsylvania
Herkimer County, New York
Hot Springs, Arkansas
St. Gothard (?),Switzerland
Table II gives the same data for the specimens of amethyst. Class i includes the
dark violet specimens, corresponding to Ridgway's 63'm-63'; class ii, violet,
63'-63'b; iii, pale violet, 63'b-63'e; and class iv, very pale violet,
63'e-colorless.&&&&&
TABLE II. LOCALITIES AND DEPTHS OF COLOR FOR AMETHYST
Color-class
Specimen number
Lake Superior district
Smithfield, Rhode Island
Serra do Mar, Brazil
Genyo,Corea
Guanajuato, Mexico
Aspen, Colorado
Schemnitz, Hungary
North Carolina
Tredell County, North Carolina
Jefferson County, Montana
Delaware County, Pennsylvania
Mahatsarakaly, Madagascar
Lincoln County, North Carolina
Iredell County, North Carolina
Hoki, JapanGuanajuato, Mexico
Guanajuato, Mexico
Specimens 17a and 17b are dark and pale portions of the same group of
crystals.&&&&&
ACKNOWLEDGEMENTS&&&&&
Grateful acknowledgement is made of the following assistance rendered during
this investigation: The Department of Physics of the University of Michigan
kindly permitted the use of a photospectrometer, and of an electroscope for some
time, and several members of the staff gave freely of their time and advice. Dr.
D. C. Bardwell, of the U. S. Bureau of Mines, radiated several sections of rock
crystal. Considerable aid in obtaining specimens was given by Dr. H. V.
Ellsworth, of the Canadian Geological S Messrs. M. G. Biernbaum, of
Philadelphia, P W. J. Elwell, Danbury, Connecticut, and W. J.
Paquette, Toledo, O the Philadelphia Academy of Natural Sciences and Ward's
Natural Science Establishment, Rochester, New York. Dr. S. C. Lind, of the U. S. Bureau of Mines, and Professor Waldemar Lindgren, of the
Massachusetts Institute of Technology, gave their advice and opinion with regard
to certain problems encountered in the work. Professors E. H. Kraus and W. F.
Hunt, of the Mineralogical Laboratory of the University of Michigan, kindly
supervised the entire investigation and made many indispensable suggestions.&&&&&
II. PHYSICAL PROPERTIES OF SMOKY QUARTZ AND AMETHYST&&&&&
Only those properties in which smoky quartz and amethyst differ from ordinary
quartz will be considered here.&&&&& COLOR - The color of smoky quartz varies from a pale and somewhat yellowish brown
(Ridgway's 19'''f), or a pale grayish brown (17''''f), through wood
brown (17''') and dark brown (13''m) to black. Amethyst is more constant
in hue, ranging from colorless to deep violet (about 63'g to 63'm).&&&&&
CRYSTAL FORM - Amethyst is nearly always well crystallized, and smoky quartz
frequently so, in contrast to the universally massive form of rose quartz.3
Smoky quartz and amethyst were crystallized slowly from aqueous solutions while
rose quartz must have formed more quickly from a pasty aqueo-igneous fusion.&&&&&
The abundant occurrence of trigonal trapezohedrons and bipyramids upon smoky
quartz crystals is testified to by numerous citations in the literature. Unequal
development of
r and z is also often noted. Amethyst, too, may show these
characters. Smoky quartz, and more especially amethyst, are often twinned, the
boundaries between the individuals in the twinned crystals being generally sharp
and quite regular. Sections of& smoky quartz or amethyst crystals are
generally free from fractures.&&&&&
These characteristics unite in indicating that smoky quartz and
amethyst were formed as the alpha or low-temperature form of quartz. (see part
III).&&&&&
ZONAL COLORING - Both of these varieties of quartz are very often zonally colored.
Indeed, amethyst almost always has a zonal distribution of color, which is of
two types, frequently combined in a single crystal:&&&&&
1. In fine lamellae parallel to the rhombohedron faces.&&&&&
2. A type best revealed by a basal section, which shows a division into sectors.
One half of these are violet, and all the other sectors, alternating with those that are violet, are either colorless, yellow,
or smoky.&&&&&
The optical anomalies arising from the intimate twinning of the right and left
lamellae and sectors, which correspond to the differently colored areas, are
well described and illustrated by Tutton (51, 57). Intergrowths of smoky quartz
and amethyst are frequent.&&&&& DICHROISM - The absorption of smoky quartz is
e&o, and the dichroic colors are
as follows, depending upon the depth of color:
slightly brownish yellow
pale pure brown
dark yellowish brown
pure brown
very dark brown
The pleochroism of rock crystal which had been colored brown by radium
radiations was found to be identical with that of natural smoky quartz.&&&&&
In amethyst the dichroism is less uniform than in smoky quartz, due to the usual
zoning of the colors. The specimens examined showed (1) reddish purple to
purple, and (2) purple, bluish purple, or indigo. In some cases no dichroism was
apparent. Haidinger (4) made an extensive study of the pleochroism of
amethyst, and his results show the absorption to be
e&o, with the color for
more reddish than that for o.&&&&&
INDICES OF REFRACTION - The variation of the indices of refraction with the color
in quartz has been studied by Forster (7), Dufet (13), Hlawatsch (17), and
Wülfing (30). The values which these investigators found for amethyst (&
to 1.54427) lie entirely within the range for rock crystal (& 1.54418
to 1.54433). The index of an amethyst from Uruguay was increased 5 x 10-5, by
heat-decolorization, according to Wülfing. Most of the measurements for smoky
quartz agree closely with those of the other two varieties. In the fifteen
determinations recorded for smoky quartz the value for & was between 1.54403 and
1.54436 fo in the other two cases
was given as 1.54387
and 1.54388, respectively. Wülfing and Forster found that the heat-decolorization
of dark smoky quartz caused no change in the index of refraction, but Hlawatsch
noted a slight increase in the fourth decimal place Even the largest variation
in refractivity from one specimen of smoky quartz to another is very slight, rarely attaining a
magnitude of several units in the fourth decimal place.&&&&&
It is unlikely that the pigmenting impurities constitute any large proportion of
the total impurities which effect the optical properties of these types of
quartz. For this reason it is impossible to draw any plausible conclusions as to
the nature of the pigments from this type of evidence.&&&&&
III. OCCURRENCE AND GENESIS OF SMOKY QUARTZ AND AMETHYST&&&&&&
The production of the
characteristic color of such minerals as smoky quartz and amethyst is due to the coexistence of the proper chemical and
physical environment in the solutions from which they form. It is necessary that
there be present those chemical compounds which constitute the pigment, and it is just as imperative that the
mineral crystallizes under favorable physical conditions. Temperature is
probably the most important of the physical factors. At this point in the study
an effort will be made to determine the chemical and physical conditions
prevailing during the formation of smoky quartz and amethyst.&&&&&
OCCURRENCE&&&&&
The occurrences of smoky quartz and amethyst may conveniently be classified into
the six groups discussed below. With the exception of the last, they are
arranged in the most probable order of decreasing temperature and pressure
conditions.&&&&&
1. IN CAVITIES IN DEEP-SEATED IGNEOUS ROCKS, PRINCIPALLY PEGMATITES
- Both amethyst and smoky quartz occur frequently in the deep-seated
igneous rocks, especially in the drusy cavities of pegmatites. These minerals
crystallized out from hot aqueous solutions containing a large amount of carbon
dioxide and other mineralizers. Quartz crystals generally coat the walls of the cavities and are among the last differentiates from the magma.&&&&&
Smoky quartz occurs in a wide variety of pegmatite types, comprising: (a) those with potash feldspar (e.g., Madagascar); (b) gem beryl
pegmatites (Mourne Mountains, Ireland); (c) the Li-F-B type, with gem tourmaline and lepidolite (Mount Mica, Maine); (d) the
Li-F-Mn-phosphate type (Branchville, Connecticut); (e) the cassiterite and tourmaline pegmatites
(Fichtelgebirge); (f) the
Cb-Ta-U-rare earth pegmatites, with radioactive minerals (many localities in
Ontario).&&&&&
Smoky quartz is also found in the body of pegmatite veins, where it was often
the last constituent to crystallize.&&&&&
Amethyst is less abundant in pegmatites than smoky quartz and it is not found in
the body of the pegmatite veins, but occurs only in the cavities. The drusy
cavities containing amethyst and smoky quartz are not confined to pegmatites,
though they are most abundant there. Similar pockets often occur in granites, as
well as in other deep-seated rocks.&&&&& 2. IN HYDROTHERMAL VEINS CLOSELY ASSOCIATED WITH GRANITES AND
PEGMATITES - These
quartz veins were formed by the silica-bearing aqueous solutions which were the
last differentiation products of acidic magmas. Amethyst and smoky quartz are
sometimes found in cavities in such veins.&&&&&
3. IN THE ALPINE TYPE OF VEINS - The Alpine veins have been thoroughly studied by
Koenigsberger (24, 41, 44). They were formed by hot, ascending waters, rich in
CO2, which leached out the constituents of the rocks through which they passed.
The dissolved substances later crystallized out in new combinations. Naturally,
the composition of the minerals thus formed was determined by the nature of the
leached rock.&&&&&
Smoky quartz is abundant in these veins, while amethyst is not infrequent. Smoky
quartz is found in the veins in adularia gneiss, biotite gneiss, granites, and
acid like rocks, but the quartz in the veins traversing schists of sedimentary
origin and basic igneous rocks is almost always colorless. The most important
associates of smoky quartz are as follows: (a) formed before or with the quartz:
and (b) formed after the crystallization of the smoky quartz: fluorite
characteristically red, calcite, the zeolites, and chlorite.&&&&&
Koenigsberger (24) states that in the central Alps the intensity of color of the
smoky quartz crystals depends upon the altitude of the occurrence. He gives the
following data for the western part of the protogene:
m. altitude
the quartz is colorless
a brown color is noticeable
distinct brown color
the typical smoky quartz begins
deep colored morion
Brauns (37) thinks that the color may have been due to radium and that the
radium may have been more active at higher levels, or that a lower temperature in the higher rocks permitted a more intense color
to be produced by the radium. Most probably the explanation lies in a
temperature effect. If the present altitude of the occurrences represents the
proportional depth of the quartz when it was formed, the temperature of the
veins now at 1400 m., would at that time have been 45° more than that of the
veins now at 2900 m., assuming an added temperature of 1° for each increment of
33 m. in depth. This is a sufficient temperature range to allow the production
of the different degrees of color observed (see part V).&&&&&
Amethyst in the Alps is always accompanied by iron minerals. Limonite is the
most frequent associate, others being ankerite, siderite, and chlorite.&&&&&
4. IN ORE VEINS - Colored quartz is not infrequently found in metalliferous veins.
Amethyst occurs in such deposits more often than the smoky quartz. Amethyst has
often been noted in the silver veins which Lindgren5 describes as &deposits
formed near the surface by ascending thermal waters and in genetic connection
with igneous rocks.& Examples are the deposits at Schemnitz, Hungary, and
Guanajuato, Mexico. It is also noted in the ore-bodies classified as
metalliferous deposits formed at intermediate depths, as, for example, in
the lead-silver veins of Pribram, Bohemia, and in the silver veins on the north
shore of Lake Superior. Such minerals as the carbonates, the sulfides, barite,
and fluorite are common associates of amethyst in ore veins.&&&&&
When smoky quartz is found in ore veins it is generally in those which are
mineralogically related to pegmatites, such as the cassiterite veins of Saxony.&&&&&
5. IN THE AMYGDALOIDAL CAVITIES OF BASIC IGNEOUS ROCKS - Amethyst is very
frequently found in the cavities of basic eruptive rocks. The associated
minerals are agate and chalcedony, formed earli and
datolite, prehnite, pectolite, apophyllite, the zeolites, and calcite, formed
later. In some localities it seems evident that these minerals were precipitated
from magmatic liquids in the gas cavit in others they were
formed by the action of atmospheric waters percolating through recently erupted
lava flows.&&&&&
Amethyst is found in veins and geodes in the Triassic traps of New Jersey, the
Connecticut Valley, and Nova Scotia. Smoky quartz is only occasionally noted in
these rocks. Another well known occurrence for amethyst is in the chalcedony and
agate geodes from melaphyres in Brazil and Uruguay.&&&&&
C. RELATIVELY UNIMPORTANT MISCELLANEOUS OCCURRENCES&&&&&
A few occurrences of amethyst and smoky quartz in calcareous rocks, sandstones,
and quartzites, in which there was no known genetic connection with igneous
rocks, have been reported. In these instances the quartz crystals must have been
deposited by waters of only moderate warmth. Amethyst often occurs in the
agatized trees of Yellowstone Park and Arizona, the silicification having been
caused by cool waters of meteoric origin.&&&&&
ELEMENTS ASSOCIATED WITH SMOKY QUARTZ AND AMETHYST&&&&&
Many other elements occur in the silica-bearing solutions from which these
varieties of quartz crystallize. Minerals containing the following elements are
frequently found with both smoky quartz and amethyst: H, C, as CO2,
very common both as a g Na, K, Ca, Mg, Fe, Mn, Al, and Si
in the alumino-si F, in fluorite, apatite, apophyllite, and
B, in tou and Ti in the always present rutile
inclusions, and as anatase and brookite.&&&&&
Many of the rarer elements are more characteristically associated with smoky
quartz than with amethyst. These include: the less common alkalies, Li, Rb, and
Cs, in lepidolite, tourmaline, alkali beryl, Be, P, in
Sn, W, Mo, in
and in the numerous rare earth and radioactive minerals: Cb, Ta, Th,
U, Ra, the rare earths, and Zr.&&&&&
The frequent occurrence of smoky quartz in association with rare earth and
radioactive minerals is very significant, for later it will be indicated that
smoky quartz may have been colored through the action of radioactive elements.
In Ontario smoky quartz is a constant associate of radioactive minerals,6 and
the same association is frequent in Madagascar.7 Enormous smoky quartz crystals
occur in the well known radioactive pegmatite of Baringer Hill, Texas.&&&&&
Only very pale varieties occur elsewhere than in acid igneous rocks, which are
much more radioactive than other types of rocks.8 There is, therefore, a
correlation between the occurrence of smoky quartz and the radium content of the
rocks in which it is found.&&&&&
Amethyst is often accompanied by minerals of some elements rarely found with
smoky quartz: S, As, Cu, Zn, Pb, Ag, and Au, in the sulfides, sulfo-salts, and
Ba, the compounds of Fe, limonite, goethite, hematite,
and siderite, which are the most characteristic associates of amethyst,
especially the darker varieties. One of these iron minerals invariably
accompanies amethyst in the Alps (24, 41, 44). Amethyst is associated with
limonite veins in Lincoln County, North Carolina. It occurs on siderite at
Macskamez? in the Siebenbürgen, and on carnelian containing 3 per cent Fe2O3 in
the &Buntsandstein& of Waldshut, Baden. At Hüttenberg, Carinthia, it
is found as druses on siderite and limonite. Near Onega-See, Russia, amethyst
enclosing goethite needles is found.&&&&&
A specimen from El Paso County, Colorado, was zoned in smoky brown and violet.
There were a. few scattered needles of goethite in the smoky area, but the
violet portions are literally crowded with them.&&&&&
In the Lake Superior district much of the amethyst has inclusions of hematite or
goethite. In specimens examined the color was deepest for several mm. below the
thin layer of hematite inclusions, the rest of the crystal being white or
colorless. These relations indicate that the violet quartz began to be formed
when a sufficient concentration of iron was attained in the mineral solutions,
the quartz previously formed being colorless. As the amount of iron increased
the color became darker, and finally the deposition of hematite took place. In
Madagascar (49) also, red and black hematite inclusions occur in amethyst.&&&&&
Many more instances of the occurrence of iron minerals with amethyst might be
cited. It is significant that the amethyst from amygdules in basic igneous rocks
is usually very dark, while that in pegmatites and related veins is most apt to
be pale. Basic igneous ro acid rocks are low.&&&&&
While many elements occur in the solutions from which amethyst has been
deposited, iron is the only pigmenting substance which is characteristically
present. The facts presented in the preceding paragraphs are good evidence that
iron is essential in
producing the color, a conclusion which data given later will substantiate.&&&&&
The chemical factors necessary in the formation of smoky quartz and amethyst,
aside from the presence of the compounds causing the colors, are a moderate
amount of uncombined silica in the aqueous solution, with considerable carbon
dioxide and other mineralizers. With too great a concentration of silica the
cryptocrystalline or poorly crystallized varieties of quartz are likely to be
formed. At temperatures within the formation range of opal, the presence of
carbon dioxide seems to favor the growth of quartz instead of opal.9 &&&&&
PARAGENESIS&&&&&
The paragenetic relationships of smoky quartz, amethyst, and the more important
associated minerals are shown in Table III. Very little additional discussion is
necessary. These varieties of quartz were generally formed after the colorless
or white quartz of the pegmatites in which they occur, and after the chalcedony
and agate of basic rocks. In the first instance, this is due to the temperature,
which at first is too high to allow the pigmenting of the quartz. In the basic
rocks, the cryptocrystalline varieties are at first precipitated from the
concentrated silica solutions, to be followed later by the more slowly formed
crystals.&&&&&
TABLE III. PARAGENESIS OF SMOKY QUARTZ AND AMETHYST
Time of formation relative to that of smoky quartz and amethyst
Afterwards
Orthoclase, microcline, albite
Tourmaline, beryl, micas
Rare earth minerals
anatase, brookite
Hematite, limonite, goethite
Calcite, chlorite
apophyllite, pectolite
Colorless or white quartz
Agate and chalcedony
X indicates &generally&&&&&&&&&
x indicates &occasionally&&&&&&
TEMPERATURE OF FORMATION&&&&&
The minimum temperatures at which decolorization occurs is shown in part V to be
approximately 225° for smoky quartz and 260° for amethyst. It will be of
interest to ascertain whether other lines of evidence unite in indicating a
formation temperature below the point of decolorization.&&&&&
CRYSTALLOGRAPHIC EVIDENCE - Wright and Larsen10 have indicated criteria which
may be used to distinguish quartz formed above 575° from quartz formed below
that temperature. As shown by the description of the physical properties in
section II, the application of these criteria to smoky quartz and amethyst prove
unquestionably that they were formed below 575°, as the alpha modification of
quartz.&&&&&
EVIDENCE FROM LIQUID AND GASEOUS INCLUSIONS - Quite precise information concerning
the temperature and pressure conditions during the formation of smoky quartz and
amethyst is afforded by the abundant liquid-gas-filled cavities.&&&&&
From an extensive study of artificial and natural crystals, Sorby11
concluded that &at the temperature at which they were formed, the fluid
cavities in crystals are full of fluid, and . . . . at a lower temperature they
contain vacuities, owing to the contraction of the fluid on cooling . . . . .
The temperature (of formation) . . . . might be ascertained by determining what
increase of heat would be required to expand the fluid so as to fill the
cavities.&&&&&&
Much more recently, Johnsen (47) by the application of accepted physico-chemical
relations, has been able to construct a temperature-pressure curve, at some
point along which an amethyst crystal studied by him must have been formed.
This crystal contained a cavity filled with CO2. At 20° both liquid and gaseous
phases of CO2 were present in the ratio of 70 to 30 by volume, respectively. At
30°, approximately the critical temperature of CO2, the whole inclusion became gaseous. From the volume ratios of the two
phases at 20° and their known densities12&
Johnsen calculated the density of
the originally included CO2 gas to be 0.60. Using van der Waal's equation, he
then calculated the pressure-temperature curve along which carbon dioxide would
have that specific gravity. (This is the curve
ab of Figure 2 in this
paper). The amethyst crystal in question must undoubtedly have formed at a
temperature and pressure falling at some point on the curve, but one quantity
must be known if the other is to be found.&&&&&
It appeared that both the temperature and pressure under which a specimen of
quartz was formed could be approximately determined if the mineral contained
both water and carbon dioxide inclusions. Examination of a series of crystals
showed that such is not infrequently the case. These gaseous and liquid
inclusions may be classified into three types, as follows:&&&&&
1) INCLUSIONS CONSISTING OF WATER ALONE, OR OF AN AQUEOUS SOLUTION, BUT WITH NO
FREE CARBON DIOXIDE - Such cavities contain small contraction bubbles, due to the
cooling of the liquid from its temperature when enclosed in the growing quartz
crystal The temperature at which the bubble just disappeared
was determined. This is practically equal to the formation temperature, for the
slight effect of pressure may be disregarded.
FIG. 1&&&&&
The fragment of quartz under examination was placed in a bath of melted
paraffine, contained in a crystallizing dish on a microscope stage. The
temperature of the bath, measured with a mercury thermometer, was gradually
increased by means of a current passed through a small platinum resistance coil
immersed in the liquid. The temperature at which a bubble in a cavity just
vanished could thus be readily determined.&&&&&
In Fig. 1, sketches a, b, c, and d, made at room temperature, illustrate this
first type of inclusion. In
a and b, from smoky quartz No 14, the bubbles
disappeared at 205±5°; in
c and d, from amethyst No. 9, at 240± 10°.
Negative crystal cavities are illustrated by
b and d.&&&&&
2) INCLUSIONS CONSISTING ENTIRELY OF CARBON DIOXIDE - Below the critical
temperature, 31°, these frequently contain both the liquid and gaseous phases.
Following Johnsen's method it is possible to construct a pressure-temperature
curve, passing through the point at which the specimen must have formed. In
Figure 2 are given the pressure-temperature curves for several densities of CO2.&&&&&
g and h, Figure 1, from fragments of amethyst Nos. 12 and 11,
respectively, illustrate inclusions entirely of CO2. The inner bubble is
gaseous, the outer zone liquid CO2. The sketches show the conditions at room
temperature. Above 31° there is only one phase, gaseous CO2.&&&&&
3) INCLUSIONS OF WATER WITH BUBBLES OF CARBON DIOXIDE AND WATER VAPOR - The CO2 in
the cavity exceeds the amount soluble in water. Below 31° it may be either
entirely gaseous CO2 or may exist as two phases. These
CO2 bubbles in water
furnish the same kind of information as is given by those inclusions entirely of
The carbon dioxide bubbles can be distinguished from the contraction bubbles
since the ratio of CO2 bubble to liquid is quite variable from one cavity to
another in a single fragment, while in bubbles due solely to contraction the
relation is necessarily quite constant. Undoubtedly, the CO2 in this third type
must have been enclosed in the quartz as bubbles in the water.&&&&&
Bubbles of CO2 in water are illustrated by diagrams
f (smoky quartz No.
15) and by i, a negative crystal cavity (smoky quartz No. 4). In the cavities
represented here the density of the CO2 is such that it all remains gaseous at
room temperature.&&&&&
When the first together with either the second or third types of inclusions
occur in the same specimen, both the temperature and pressure at the time of
formation are easily determinable. The water inclusions give evidence as to the
temperature, which enables the pressure to be determined from the
temperature-pressure curves afforded by the CO2 inclusions. The temperature
determination is the more accurate because it involves no calculation.&&&&&
The cavities sketched in
j and 1, Figure 1, at 25° are of the first and third
types, respectively, and they occurred in the same crystal (smoky quartz No 5)
The contraction bubble in
j disappears at 135±°. Sketches
l are of the
same cavity at different temperatures. In k, the temperature is greater than 31°, when all the
CO2 is gaseous. In
l the innermost zone is a globule of liquid
CO2 at the
interface between the gaseous CO2 and the outermost zone of water.13&&&&&
In the table given below are tabulated the results of examining a number of
specimens of amethyst and smoky quartz in this way.&&&&&
TABLE IV. TEMPERATURE (t) AND PRESSURE. (p) OF FORMATION OF SMOKY QUARTZ AND
AMETHYST AS DETERMINED FROM THEIR LIQUID AND GASEOUS INCLUSIONS
SMOKY QUARTZ
Up to 2504
1 Smoky gray crystals in a water
filled geode, Uruguay. C. W. Gumbel, Sitzb. k. Bayr. Akad. Wiss.,
Math. phys. Cl.,10, 241-254 (1880).
2 G. W.Hawes, Am. J. Sci., 21, 203-
209 (1881) also has studied crystals
from this locality. From his data&
the writer finds:
t 110-114°,
500 atm.?&
3 Smoky quartz from Alpligengletscher. J. Koenigsberger,
Neues Jahrb Mineral.
Geol., Beil.-Bd., 14, 43-119 (1901).
1 A cut gem, locality unknown.
2 Very pale crystal from Schemnitz, with a macroscopic bubble.
<font SIZE="3" FACE="Times Roman" COLOR="#Mursinka,
<font SIZE="3" FACE="Times Roman" COLOR="# Assuming t & 150°
<font SIZE="3" FACE="Times Roman" COLOR="# Assuming t=200°
Figure 2 illustrates the paragenesis of smoky quartz, amethyst, and carbon
dioxide. It is based on Johnsen's work, with. adaptations and much added data.
The normal geothermobar, as shown, is that for a temperature increase of 1° per
33.3 m. increase in depth, and a pressure rise of 1 atm. per 4 m. The depths in
the earth's crust are indicated at intervals of 2 km along this curve. The
pressure-temperature curves for several densities of CO2 are given. To the right
of these curves the corresponding proportion of liquid CO2 existing at 20° is
indicated, in terms of its volume percentage of the whole inclusion of CO2. The
vapor pressure-temperature curve for water is also given.&&&&&
&FIG. 2&&&&&
The probable pressure-temperature conditions under which amethyst forms are
represented by the area which is obliquely ruled, while the hypothetical region
of formation of smoky quartz is shown by horizontal lines. It is obvious that
amethyst is formed under a greater temperature and pressure range, both higher
and lower, than smoky quartz, and that the two types may form simultaneously
through a considerable variation in temperature and pressure, as frequently
happens.&&&&&
The diagram (Fig. 2) shows that both of these varieties of quartz were formed
under either lower pressure or higher temperature than normal for the earth's
crust, or under both lower pressure and higher temperature. The latter is most
probable. Those are the conditions to be expected in pockets containing hot
aqueous solutions. The open cavities relieve their contents of the normal pressure, while the solution is hotter than the normal temperature
because of its magmatic origin. The actual pressure must be that of the water
vapor and gases. The pressure is shown by the inclusions to exceed that which
would be caused by the water vapor alone at the several temperatures.&&&&&
EVIDENCE FROM PARAGENESIS - In respect to the formation temperature, the
paragenetic relationships of these two colored varieties of quartz agree with
the evidence from the inclusions. Adularia, formed before or with the earlier
formed crystals of smoky quartz, is frequently deposited by waters of
50-150° in temperature, according to Lindgren.14
Doelter15 concludes that
orthoclase may have formed at temperatures as low as 100°. Both albite and
orthoclase have been found in sedimentary rocks under circumstances positively
demonstrating their formation after sedimentation.16 Muscovite, also of an
earlier stage than smoky quartz, has been synthesized at 196-233°. Therefore,
the lowest possible formation temperature for these earlier-crystallized
minerals lies well below the highest possible temperature of formation for smoky
quartz and amethyst, as indicated by the inclusions and the decolorization
experiments.&&&&&
Calcite, fluorite, and chlorite, minerals of a later stage than smoky quartz and
amethyst, are capable of formation through a rather wide range, down to very low
temperatures. The zeolites are stable in a more restricted region and are
characteristically low temperature minerals. They have been synthesized at
temperatures as low as 100°, and in nature have been formed at even lower
temperatures. Phillipsite, for example, is found in deep sea muds. The zeolites,
fluorite, calcite, and chlorite could well have been formed below the lowest
temperatures indicated for smoky quartz and amethyst.&&&&&
SUMMARY&&&&&
It is shown that amethyst and smoky quartz were crystallized from hot aqueous
solutions in cavities, under less pressure than normal for the depth at which
they were formed, and in a temperature range of about 110-220° for smoky
quartz, and 90-250° for amethyst. The crystals grew rather slowly, from not too
highly concentrated solutions. These solutions contained many other compounds than
silica, notably carbon dioxide and other mineralizers. Smoky quartz is
frequently accompanied by radioactive minerals. The iron minerals, hematite,
limonite, goethite, and siderite are generally found with amethyst.&&&&&
IV. RADIATIONS AND THE COLOR OF SMOKY QUARTZ AND AMETHYST&&&&&
Much has been published concerning the effects of radiations on the color of
smoky quartz and amethyst &#91;Doelter (32, 33, 38, 39, 40, 42, 53), Egoroff (27),
M. Berthelot (28), Miethe (29), D. Berthelot (31), Phillips (35), Simon (36),
Brauns (36), Newberry and Lupton (45), Meyer and Pribram (50), and Lind and
Bardwell (54)&#93;. For the present investigation Dr. Bardwell kindly exposed three
sections of New York rock crystal to the penetrating radiations from 230 mgs.
Ra. for 112 days. The dichroism and absorption spectraum of these artificially
colored specimens were found to be identical with that of the natural smoky
quartz (see sections II and VI).&&&&&
The many investigations which have been reported by various workers allow very
general conclusions to be made:&&&&&
a) The color of heat-decolorized amethyst and smoky quartz is restored by the
penetrating radiations from radium.&&&&&
b) Pale specimens may have their colors intensified in the same way, but
sometimes amethyst becomes brown on radiation.&&&&&
c) Colorless quartz normally becomes smoky brown, but sometimes is rather
resistant to coloration by radium, and rarely becomes violet.&&&&&
d) A zonal coloring like that observed in naturally colored quartz crystals is
sometimes produced by radiation.&&&&&
e) The radium-induced colors are unstable at moderate temperatures, and radiated
specimens usually phosphoresce when heated.&&&&&
RELATION BETWEEN RADIUM RADIATIONS AND THE PIGMENTS OF SMOKY QUARTZ AND AMETHYST&&&&&
There is good evidence that the smoky brown color produced by the radiation of
rock crystal is identical with the coloration of natural smoky quartz. The
artificially colored variety agrees exactly with the natural in hue, dichroism,
and absorption spectrum. Furthermore, the zonal coloring observed in natural crystals is often
duplicated in the radiated rock crystal. Both artificial and natural smoky
quartz are decolorized at moderate temperatures. These facts suggest that the
pigmenting of natural smoky quartz is due to the radiation of colorless quartz
by radioactive substances in the solutions from which it formed. This hypothesis
will be further supported and elaborated.&&&&&
On the other hand, it does not seem possible to trace any inevitable connection
between the action of radium and the natural production of the amethystine
color. Radiation of almost any specimen of quartz, such as rock crystal, or rose
quartz, or frequently even amethyst itself, brings about the brown coloration.
On the contrary, the violet color is very rarely produced except when the color
of pale or heated amethyst is deepened by radiation. The color of amethyst must
be due to some characteristic pigmenting impurity, which other parts of the
present study indicate to be a ferric compound.&&&&&
HYPOTHESES PROPOSED TO ACCOUNT FOR THE COLORATION OF MINERALS BY RADIATIONS&&&&&
The explanations which have been advanced to account for the production of color
by the radiation of a mineral fall into two main classes:&&&&&
1. The color is due to the formation of colloidal particles.&&&&&
2. The color is due to the liberation of electrons without the production of
colloidal particles.&&&&&
Doelter (40, 42), especially, has supported the first view. According to his
view colorations are probably due to the formation of colloidal particles by the
disintegration of impurities or of the pure mineral substance itself. The size
and degree of dispersion of the resulting particles would determine the color
produced, as in any other colloidal solution. Doelter suggests colloidal sodium
or lithium, derived from included silicates, as the pigments in smoky quartz and
amethyst. Decolorization by heating would be due to a change in the size of the
particles or of their dispersity. Wild and Liesegang (52) have pointed out that
it is very difficult to accept the hypothesis that solid colloidal particles
might migrate through the rigid crystalline framework of a mineral.&&&&&
Lind and Bardwell (54) have recently proposed a theory which seems much more
probable: Certain groups of electrons are thrown into metastable positions by the radiations. No displacement of the atom
is involved, nor are any colloidal particles produced. Their assumption is that
the displaced electrons are able to vibrate with a frequency which may fall in
the visible region, causing the production of a color. They may return to their
normal positions under the influence of heat.&&&&&
SCATTERING OF LIGHT BY SMOKY QUARTZ AND AMETHYST&&&&&
Strutt (46) has observed that a ray of light passing through a section of smoky
quartz is strongly scattered, the path of the light being visible. In clear,
colorless quartz, however, there was no scattering. Raman (48) has made similar
observations.&&&&&
Vanzetti (55, 58) found the light-scattering in morion to be pronounced. After
decolorization of the section at 300° the path of the light ray was no longer
visible. In a zonally banded section light was scattered by the brown bands, but
not by those which were colorless. Vanzetti concluded that it was plausible to
suppose that the light-scattering and the color, both destroyed by beating and
restored by radiation, were due to a colloidal suspension whose particles might
vary in size. Perhaps a partial decomposition of the SiO2 was involved.&&&&&
Some observations made during the present study verify Vanzetti's experiments on
smoky quartz The scattering of light from quartz was found to be of three types:&&&&&
1. From microscopically visible cavities and inclusions. Common to all quartz,
and unaffected by heat. 2. From long narrow areas of scattering particles.
Noticeable in rock crystal as well as in smoky quartz. Neither of these first
two types concern the color. 3. The third type of light-scattering has a
connection with the color. It is impossible to detect any microscopically
visible particles which could be responsible for this effect. There is a general
scattering in the entire path of the beam. In the following paragraph only this
type is considered.&&&&&
Eight specimens of smoky quartz were examined for this phenomenon. The effect
was decidedly stronger in the darker specimens. From each of two specimens of
smoky quartz (Nos. 6 and 8) pairs of sections were cut from single crystals. One
section of each pair was decolorized by long and gentle heating, while the
other was reserved for comparison. In both cases the original section scattered
light strongly while the decolorized section showed little or no scattering. It is very evident, then, that the coloration of
smoky quartz is to be correlated with the scattering of light by microscopically
invisible particles, which were probably produced by the action of radioactive
substances.&&&&&
It seems probable that the particles are of atomic rather than colloidal size.
There are great difficulties to be met in explaining the migration,
agglomeration, and dispersion of colloidal particles in a crystalline structure.
As shown by evidence to be given later the pigmenting and light-scattering
particles may well be atoms of elemental silicon.&&&&&
In seven amethyst specimens there was no light-scattering, which is further
evidence opposed to coloration by colloidal alkalies, the theory which has been
proposed by Doelter (40, 42).&&&&&
SUMMARY&&&&&
The evidence given thus far is in agreement with the theory that smoky quartz
owes its color to atoms of silicon, formed by the disintegration of silica,
through the action of radium radiations. The mechanism of the formation of the
free silicon may perhaps be pictured in this way: The radiations may remove the
four outer electrons from a silicon atom, which would then be equally shared by
the two associated oxygen atoms. As a result, two free oxygen atoms and a free
silicon atom would be formed. They could take no part in the crystal structure
since their attractive force for other atoms would have been destroyed. Hence,
they should act as small inclusions, the silicon atoms producing the
light-scattering and the color so characteristic of smoky quartz. We would
expect the silicon atoms to be most effective in scattering light because of
their greater atomic weight, and the possibility of the escape of the oxygen
atoms.&&&&&
V. THE COLOR CHANGES CAUSED BY HEATING&&&&&
Several investigators have made rather detailed studies of the heat-decolorization
of smoky quartz and amethyst. The usual method of study has been to gradually
increase the temperature, noting the points at which the various changes in
color occur.&&&&&
But, with longer heating at a constant temperature, the decolorization takes place at a lower temperature than that given by the
first method. Therefore it was thought desirable to more thoroughly investigate the influence of long-continued heating upon the
decolorization. This new data, combined with the large number of observations
reported by other investigators, affords, quite a complete knowledge of the
effect of heat upon the colors of smoky quartz, and amethyst.&&&&&
REVIEW OF THE LITERATURE&&&&&
Simon (36) and Herman (34) have investigated the decolorization of these
minerals in various reducing and oxidizing atmospheres. They found that the
surrounding gas had no influence on the color changes in smoky quartz and
amethyst.&&&&&
Simon worked with a large number of specimens and heated them both in hydrogen
and oxygen. In. smoky quartz the first change was to a smoky- or greenish-gray.
The mineral began to be decolorized at 300° and decolorization was complete at
330-370° in less than an hour. Heating for 48 hours at 290° also caused
complete loss of color. With amethyst there were several distinct color changes
as the temperature was increased. At 170-210° the specimens became gray violet.
The change to colorless began at about 300° and was complete at 400 to 500°. A
yellow coloration frequently superseded the colorless stage, and finally, above
700°, the specimens became milky white.&&&&&
Hermann (34) heated specimens of smoky quartz and amethyst at about 700° for
two hours in the following atmospheres: air, oxygen, illuminating gas, sulfur
vapor, hydrogen, nitrogen, ammonium chloride vapor, and ammonia gas. The color
of all amethyst specimens changed from the original hue through gray-violet and
yellow stages to opalescence. All the fragments of smoky quartz became colorless
and clear.&&&&&
Wild and Liesegang (56) have recently investigated amethyst. All of the
specimens became colorless by 500°, and on further heating became milky. The
darker specimens often became smoky yellow, while the paler ones changed to
clear yellow. One specimen, studied in detail and heated in air, began to be
decolorized at 180-200°, was completely colorless at 340°, and became pale
yellow at 350°.&&&&&
Less detailed work has been done by other investigators. Heintz (6) decolorized
a specimen of dark amethyst at 250°. Berthelot (28) found the decolorization
temperature of an amethyst to be 300°. The color of deep black morion was lost
at 290°, according to Forster (7). Koenigsberger (21) found the decolorization
temperature of smoky quartz from several localities to be 295° after six to seven
hours, and 370° after several minutes of heating. He also completely
decolorized a specimen of smoky quartz in a bomb at 400° and 400 atmospheres
NEW OBSERVATIONS&&&&&
In the measurements made at 235 ± 10°17 and at 240± 10° the fragments of
quartz, from one to three cm. in diameter, were heated on an electric hot plate
in a pyrex flask. A thermometer was inserted through the pierced cork, its bulb
being placed beside the fragments. For the determinations at higher
temperatures, a small electric oven was constructed. The temperatures were
measured by means of a mercury thermometer.&&&&&
TABLE V. HEAT-DECOLORIZATION OF SMOKY QUARTZ&&&&&
Explanation of table. - At each different temperature (i.e. 235°, 275°, etc.) new
specimens were taken. The colors are given in Ridgway's terms, and they are also
designated by less exact but more readily understood terms. The colors were
determined both when the specimens were hot and after they bad cooled to room
temperature.
Temp during heating
Time of heating
Total time of heating
Color noted at:
Resulting color
Specimen No. 8
Specimen No. 6
Original color
13&1; medium dark brown
13&n; very dark brown
P yellowish-greenish
P dark greenish
As originally
As originally
19 hrs. more
25'''g; pale greenish yellow
&21''''1; dark
greenish brown
15''''d; pale brown&
13''m; dark brown
15 hrs. more
P yellowish
19''''i; greenish brown
faintly brownish
13''m; dark brown
21 hrs. more
19''''; greenish
15'''j; medium dark
23 hrs. more
As above, has become stable
.....................
.....................
15'''a; medium brown
69 hrs. more
.....................
21'''g; almost colorless
15''''a-b; medium brown
Very pale greenish yellow&
15''''c; pale brown
2 hrs. more
Almost colorless
faint trace of brown
21'''j; deep grayish olive
15''''k; medium dark
23 hrs. more
A slightly green
15''''c; pale brown
slightly greenish
21''''a; greenish brown
15''''e; pale brown
15''' medium dark brown
2 hrs. more
P slightly brownish
15''''c; pale brown
Almost entirely colorless
18 mins. more&
Greenish yellow
Pale brown
12 mins. more
30 mins. {sic}
Greenish yellow
19'''f-g; very pale
yellowish brown
Entirely colorless.
TABLE VI. HEAT-DECOLORIZATION OF AMETHYST&&&&
Temp during heating
Time of heating
Total time of heating
Color noted at:
Resulting color
Specimen No. 6
Specimen No. 8
Specimen No. 9
Original color
63'; medium vt.
64 'b; medium
64'e; pale vt.
62 ''f; pale gray vt.
60''e; pale gray vt.
59&f; pale gray vt.
64'b; medium
As originally&
As originally&
66 hrs. more
59 ''f; pale gray vt.&
60''e; pale gray vt.&
59''f; pale gray vt.
65'd; pale vt.&
As originally
As originally
Pale gray vt.&
Pale gray vt.&
As originally&
As originally&
45 hrs. more
57'''g; very pale gray vt.&
Practically color less
64'd-e; pale vt.&
64'g-; very pale vt.
22 hrs. more
Practically colorless&
Practically colorless&
64'd-e; pale vt. &
64'g-;very pale vt.&
1 1/2 hrs.
1 1/2 hrs.
Colorless&
Colorless&&
65'f; pale vt.&
Colorless&
2 hrs. more
3& 1/2 hrs.
Colorless&&
Colorless&&
Specimen No. 6
Specimen No. 5
Specimen No. 4&
Original color
63'; medium vt.&
64'c; medium
64'm; dark vt.&
21'''e; pale olive
2 hrs. more
3 1/2 hrs.
16'j; orange&
White, translucent&
Colorless to white&
Same as hot&
Same as hot&&
Same as hot&&
The decolorization of smoky quartz is plainly a time-temperature reaction. At
380-420° the decolorization is complete and immediate. Rapidly increasing time
is required to discharge the color as the temperature of heating is lowered.
Sometimes there is a tendency for the decolorization at low temperatures to be
more or less incomplete, as in the case of specimen No. 6. The almost black
original color is completely discharged at 420°, but at lower temperatures, no
matter how long the heating is continued, an increasingly greater residue of the
color remains. After being heated for eighty-one hours at 235±10°, the color
was a medium brown, which did not change after a further exposure of sixty-nine
hours at the same temperature, but the paler specimen No. 8 was brought to
practically complete decolorization at that temperature. The size of the
fragments is also a factor in the decolorization of smoky quartz.&&&&&
The following table shows the time necessary for complete decolorization of
smoky quartz at various temperatures, or for attaining a pale but stable color.&&&&&
TABLE VII. TIME NECESSARY FOR DECOLORIZING SMOKY QUARTZ AT DIFFERENT
TEMPERATURES
Temperature&
Time necessary
Almost immediate
H specimen No. 6
Almost immediate
0.1 hrs., ca.
Koenigsberger
Koenigsberger
20-30 hrs.
30-35 hrs.&
80 hrs., ca.&
Holden: No. 6
If a curve is plotted from these concordant data, time being the abscissae,
temperature the ordinates, it will be of the parabolic type. The curve is very
steep between 300 and 400°, finally merging into the vertical axis, where time
= 0. At lower temperatures the curve rapidly flattens out until it is practically
horizontal at 225°, which may be taken as the minimum decolorization
temperature of smoky quartz, and the maximum temperature at which smoky quartz
can have existed in nature (see section III). Tests on sixteen specimens of
smoky quartz, from all four of the color classes, showed that in every case the
color disappeared after heating for shorter or longer periods at 240± 10°. The
results are given in Table VIII. It is evident that there is a general tendency
for the darker specimens to require a longer time for decolorization than the
lighter ones.&&&&&
TABLE VIII. TIME NECESSARY FOR DECOLORIZATION OF SMOKY QUARTZ AT 240± 10°
When hot, smoky quartz has a pronounced yellowish-greenish to blackish-greenish
color. If the heating is not prolonged until decolorization ensues, the original
color is regained on cooling. The decolorization of smoky quartz by heat can be
explained as being due to the oxidation of silicon atoms, causing them to revert
to their original character as parts of the quartz lattice.&&&&&
The decolorization of amethyst takes place at a higher temperature than that of
smoky quartz. After eighty-two hours at 235°, only one of the three specimens
tested showed any appreciable change of color, and it lost only a portion of its
original color. After forty-nine hours at 305-315° the other two specimens were
partially decolorized, but several hours heating at 385-420° were necessary to
completely remove the color. This agrees with the results of other
investigators. For most specimens of amethyst the minimum temperature at which
the color is unstable may be given as 260±°. At lower temperatures, amethyst
is always a gray violet when hot, though it again takes on its original color
when cooled to room temperature. Further heating after the colorless stage has
been reached often produces a citrine yellow color, especially in the darker
specimens, as is well known. This is supplanted by an opaque milkiness at still
higher temperatures. The diagram below shows the approximate temperature ranges
of the various color stages.&&&&&&&&
The change from violet to yellow, on heating, may be interpreted as due to the
disintegration of a violet ferric compound to a simpler, yellow, ferric
compound, possibly the oxide. This is further discussed in part VI.&&&&&
The changes in absorption spectra caused by heating smoky quartz and amethyst
are described in the next section.&&&&&
VI. THE TRANSMISSION OF LIGHT BY SMOKY QUARTZ AND AMETHYST&&&&&
Frequently the manner in which a mineral transmits light will give a clue to the
chemical nature of the pigment. For this reason the transmission of light
through several specimens of smoky quartz and amethyst was measured. Heat
decolorized specimens were also studied in the same way, as well as a
section of rock crystal which had been colored by radium radiation.&&&&&
REVIEW OF THE LITERATURE&&&&&
Nabl (20) compared the spectra of amethyst, &burnt amethyst,& which
had been changed to yellow by heat treatment, and citrine. The amethyst
possessed an absorption maximum in the green. After its color had been changed
to yellow by heat, the absorption spectrum was identical with that of natural
citrine. Nabl concluded that the spectrum of amethyst is identical with that of
ferric sulfocyanate, and advanced the hypothesis that the violet color is due to
that compound. However, neither the character of the absorption nor the color of
ferric sulfocyanate solutions agree with those of amethyst. The maximum of
absorption of ferric sulfocyanate in amyl alcohol is at 0.516&#956;18, while in
amethyst it is at 0.53-54&#956;. The color of sulfocyanate solutions is an almost
pure red (Ridgway 72) while that of amethyst is violet (63'). Added to these
objections is the consideration that compounds of this nature have not been
found to exist among minerals.&&&&&
Vanzetti (55) found that the maximum of absorption of light by smoky quartz is
in the violet portion of the spectrum.&&&&&
NEW OBSERVATIONS&&&&&
The measurements here reported were made in the Physics Laboratory of the.
University of Michigan. The instrument used was a photospectrometer with a
variable sector disk. Polished sections, or crystals with smooth faces, were
employed in this work. The results are graphically shown in Figures 4 and 5. The
abscissae represent the wave lengths of the transmitted light in g, the
ordinates, the percentage of the incident light which was transmitted through
the sections.&&&&&
In Figure 4, Diagram 1, are given several transmission curves for a single
section of smoky quartz. Curve
la gives the transmission of ordinary light
passing through the section in a direction parallel to the vertical axis. There
is a gradual and steady increase in the percentage of incident light transmitted
as the wave length increases. The curves marked w and a were obtained by passing
plane polarized light through the section in a direction perpendicular to the
axis. These curves give the transmission for the ordinary and extraordinary
rays, respectively. The somewhat yellowish cast of the color for a is due to the
convexity of the
curve near 0.60A. The curves also demonstrate that the absorption is e&w, as
stated previously (part II). In these and later curves, too much attention must
not be paid to the absolute amount of transmitted light. The more important
feature is the shape of the curve, for the percentage of transmitted light
varies with the thickness and clearness of the section.&&&&&
FIG. 4&&&&&&&&&&
The section, the transmissibility of which is given in curve 1a, was heated at
235±10° for twenty-two hours, which caused decolorization. New measurements,
plotted in curve 1b, were then made. The direction of the passage of light is
the same as in curve la, so that the two curves are comparable. As would be
expected, the heat treatment markedly increased the transmission of light, and the transmission is about the same for all parts of the spectrum except that
it is somewhat greater in the red. This is because decolorization was not quite
complete.&&&&&
In Figure 4, Diagram 2, are given curves for three more specimens of smoky
quartz. Curve
2a is similar to la. The specimen represented by
2b was very pale,
and therefore its transmissibility is like that of heat-decolorized smoky
quartz, 1b. Curve
2c shows the transmission of
a in another section.&&&&&
The transmissibility of rock crystal which has been colored smoky brown by
radiation (diagram 3) is exactly like that of natural smoky quartz, as a
comparison of diagrams 3 and 1 shows. Even the convexity in the curve for e,
near 0.60&#956;, is found in the radiated quartz.&&&&&
Since it has been suggested19 that smoky quartz may owe its color to
dispersoid silicon, the transmissibility of a solution of colloidal silicon was
measured. This solution was}