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Ametrine

From Wikipedia, the free encyclopedia
Mineral, quartz variety
Ametrine
Ametrine fromBolivia
General
CategoryTectosilicates,quartzvariety
FormulaSilica (silicon dioxide,SiO2)
Crystal systemTrigonal
Identification
Formula mass60.08 g/mol
ColorPurple,Yellow toOrange
Crystal habit6-sided prism ending in 6-sided pyramid (typical)
TwinningDauphine law and Brazil law
Cleavagenone
FractureConchoidal
Mohs scale hardness7
LustreVitreous
Streakwhite
DiaphaneityTransparent to translucent
Specific gravity2.65
Optical propertiesUnixal (+)
Refractive indexnω = 1.543–1.553
nε = 1.552–1.554
Birefringence+0.009
PleochroismAmethyst section shows weak to moderate purple/reddish purple
"Citrine" section shows very weak yellow/orange[1]
Melting point1650±75 °C
Diagnostic featuresDistinct segments that are purple and yellow
SolubilityInsoluble in common solvents
Common impuritiesIron

Ametrine, also known astrystine, golden amethyst, or by the trade namebolivianite, is a variety ofquartz with alternating zones of purple and yellow-orange coloration. Its name is a portmanteau ofamethyst andcitrine. While ametrine is commonly referred to as a combination of these two quartz varieties, some sources claim this is not accurate.[2] Almost all commercially available ametrine is mined inBolivia.

Color

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Ametrine, as its name suggests, is commonly believed to be a combination of citrine and amethyst in the same crystal. However, sources do not agree that the yellow-orange quartz component of ametrine may properly be called citrine. Like the purple color of amethyst, the yellow color in ametrine originates from trace amounts ofiron in the crystal structure. The difference in coloration is due to the iron existing in differentoxidation states. The yellow segments have been oxidized by heat, while the amethyst segments remain unoxidized. Some sources define citrine solely as quartz with its color originating fromaluminum-basedcolor centers, similar to those ofsmoky quartz.[2][3] This definition excludes any amethyst that has been oxidized by heat. Accordingly, the yellow quartz in ametrine would not be considered true citrine.

Origin

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Naturally-occurring ametrine is sourced almost exclusively from a single mine in Bolivia.[1] Deposits also exist in Brazil and India. The different oxidation states occur due to there being atemperature gradient across the crystal during its formation. However, most ametrine on the market is created by partially heating or irradiating amethyst.[4]

Ametrine in the low price segment may stem from synthetic material. Green-yellow or golden-blue ametrine does not exist naturally. Synthetic ametrine is grown with the hydrothermal method using solutions doped with specific elements, followed by irradiation of the created crystals.[5]

Structure

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Ametrine Emerald Cut

Ametrine is composed ofsilicon dioxide (SiO2) and it is atectosilicate, which means it has a silicate framework linked together through shared oxygen atoms.

History

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Legend has it that ametrine was first introduced toEurope by aconquistador's gifts to theSpanish Queen in the 1600s, after he received a mine inBolivia as adowry when he married a princess from the nativeAyoreos tribe.[6]

See also

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References

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  1. ^ab"Ametrine Value, Price, and Jewelry Information - International Gem Society".International Gem Society. Archived fromthe original on 2025-01-19. Retrieved2025-02-02.
  2. ^ab"Ametrine".www.mindat.org. Retrieved2025-02-02.
  3. ^"Citrine".www.mindat.org. Retrieved2025-02-02.
  4. ^"Quartz (var. ametrine) | Smithsonian National Museum of Natural History".naturalhistory.si.edu. Retrieved2025-02-02.
  5. ^Vladimir S. Balitsky; Taijin Lu; George R. Rossman; Irina B. Makhina;Anatolii A. Mar’in; James E. Shigley; Shane Elen; Boris A. Dorogovin. "Russian Synthetic Ametrine," Gems and Gemology, Summer 1999, p. 122-134
  6. ^Vasconcelos, Paolo; Wenk, Hanz-Rudolf; Rossman, George. "The Anahí Ametrine Mine, Bolivia," Gems and Gemology, Spring 1994, p. 4-23

External links

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Wikimedia Commons has media related toAmetrine.
Crystalline
Cryptocrystalline
Amorphous
Miscellaneous
Notable varieties
Chalcedony
Opal
Quartz
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