Citrine

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Citrine crystal on matrix from the mine de Nespouillières , Valzergues , France
Citrine from Russia

Citrine is the yellow-colored, macro-crystalline variety of quartz . The name is derived from the Latin citrus for lemon and refers to the lemon-yellow color of this quartz variety. Depending on the origin of the citrine and the cause of the coloration, the color varies from pale green-yellow to orange to brown-orange.

Color causes

The yellow color of citrine is caused by two different mechanisms:

Iron-containing citrines get their yellowish to orange color from submicroscopic inclusions of iron (III) hydroxide oxide (FeOOH). These iron oxide particles are approx. 100 nm in size  , absorb light in the violet to blue range of the spectrum and thus color the citrine from yellow to brown-orange.

The second coloring process has not yet been clarified in all details and is similar to the color centers in smoky quartz . Quartz that contain traces of aluminum (Al 3+ ) as well as lithium or hydrogen (Li + , H + ) can be colored greenish-yellow by irradiation. These citrines are colored by lattice defects in which aluminum (Al 3+ ) has been built into the lattice position of the silicon and lithium (Li + ) or hydrogen (H + ) in one of the neighboring interstitial spaces, for example in the six-sided channels of the quartz structure. An oxygen atom in the vicinity of the aluminum ion can then lose an electron through radioactive radiation. The resulting oxygen ion with an unpaired electron (electron hole) absorbs light in the ultraviolet range of the spectrum and colors the quartz yellow.

Artificial Citrine (Burnt Amethyst)

There are essentially five types of citrine, depending on the cause and how they are colored:

  1. Natural, iron-containing yellow-orange colored citrines: They occur as citrine zones in amethysts or as citrine sectors in ametrine . Separation of submicroscopic iron hydroxide particles gives the color.
  2. Burnt, yellow to orange-brown amethysts: Amethysts of many localities (including Brazil, Uruguay, Namibia, Tanzania and others) can be converted into citrines by heating. Submicroscopic segregation of iron oxide gives the color. Depending on the origin of the amethyst, certain temperature ranges are needed to trigger this transformation. For example, Brazilian amethysts are given a light yellow color by heating to 470 ° C. If the temperature is increased to 550 to 560 ° C, the stones become bright yellow or red-brown.
  3. Burnt smoky quartz: Smoky quartz can take on the color of citrine when heated to 300 to 400 ° C.
  4. Synthetic, iron-containing quartz: Yellow to brown citrines can be grown hydrothermally . Here, too, iron, which comes for example from the surrounding steel of the hydrothermal apparatus, gives the color. Submicroscopic iron oxide inclusions, incorporation of Fe 3+ in tetrahedral lattice positions surrounded by oxygen, and incorporation of Fe 2+ in interstitial lattice sites surrounded by octahedral oxygen in the six-sided channels of the quartz structure have a coloring effect .
  5. Quartzes colored yellow by irradiation: Quartz containing aluminum can be colored yellow by irradiation. This can of course be done in the rock or artificially in the laboratory. The source of ionizing radiation in nature is the 40 K isotope as well as uranium and thorium in the surrounding rock. Quartz of the same color can also be produced from smoky quartz by tempering at 300 ° C. In both cases, the color is caused by electron defects in oxygen.
  6. Greenish-yellow irradiation color: It is also produced by irradiating natural quartz, tempering smoky quartz at 150 to 250 ° C or a combination of both processes. Spectroscopically, they differ from the quartz crystals which are colored yellow by irradiation by an additional absorption band in the violet region of the spectrum (at approx. 400 nm). Electron holes in Al 3+ -Li + defects give the color here .

Etymology and history

The original term citrine comes from Middle Latin and refers to the yellow color of lemons . He could use all yellow stones and in the 12th century initially referred to the yellow variety of zircon (also hyacinth ). From around the 16th century the term citrine or citrine was transferred to the yellow-colored, macro-crystalline quartz.

Education and Locations

Like most other quartz, citrine is mainly igneous in pegmatite with a granitic composition. Natural citrines, however, are quite rare and pale yellow with a slight pleochroism . Most of the citrines on the market are orange-yellow, burnt amethysts .

Natural citrine deposits are found in Argentina , Burma , Brazil (Maraba, Minas Gerais, Goiás, Rio Grande do Sul), France (Dauphine), Madagascar , Russia (Urals), Spain (Salamanca, Cordoba), and the USA .

Citrine zones in amethysts are known, for example, from India ( Hyderabad ) or Brazil (Minas Gerais) as well as in citrine sectors in ametrine in Bolivia (Amahi mine). Natural, burnt amethysts are known from a few locations worldwide.

use

Cut citrine, 58 carat

Like most other types of quartz, citrine is processed into gemstones . Since natural citrines are rare, however, artificial citrines made from burnt amethysts or recolored quartz are sold almost exclusively . Often such Citrine be out of date or incorrectly as Bahia- , Madeira , Palmyra- , Rio Grande Topaz and Bohemian topaz or gold topaz called. According to the trade organization CIBJO , the mineral name must also be mentioned for consumer protection reasons (gold citrine, Madeira citrine and others).

See also

literature

  • George R. Rossman: Silica: Physical Behavior, Geochemistry, and Materials Applications. Colored Varieties of the Silica Minerals . In: eter J. Heaney, Charles T. Prewitt, and Gerald V. Gibbs (Eds.): Reviews in Mineralogy and Geochemistry . tape 29 , no. 1 , 1994, ISBN 978-0-939950-35-5 , pp. 433-467 (English).

Web links

Commons : Citrine  - collection of images, videos and audio files
Wiktionary: Citrine  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. ^ Helmut Schrätze , Karl-Ludwig Weiner : Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp.  423 .
  2. ↑ a b Jaroslav Bauer, Vladimír Bouška: Gemstone Guide . Verlag Werner Dausien, Hanau / Main 1993, ISBN 3-7684-2206-2 , p. 124 .
  3. ↑ Hans Lüschen: The names of the stones. The mineral kingdom in the mirror of language . 2nd Edition. Ott Verlag, Thun 1979, ISBN 3-7225-6265-1 , p. 349 .
  4. ^ Walter Schumann: Precious stones and gemstones. All kinds and varieties. 1900 unique pieces . 16th, revised edition. BLV Verlag, Munich 2014, ISBN 978-3-8354-1171-5 , pp. 136 .
  5. ↑ Trade name search. In: epigem.de. EPI - Institut für Edelstein -prüfung, accessed on October 28, 2019 (entry of the relevant trade names required).