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Ametrine

Mineral, quartz variety

Field	Value
name	Ametrine
boxbgcolor	#9966cc
boxtextcolor	#fff
image	Ametrin from Bolivia.jpg
caption	Ametrine from Bolivia
category	Tectosilicate minerals
group	Quartz group
species	Quartz
formula	Silica (silicon dioxide, SiO2)
molweight	60.08 g/mol
system	Trigonal
color	Purple, yellow to orange
habit	6-sided prism ending in 6-sided pyramid (typical)
twinning	Dauphine law and Brazil law
cleavage	none
fracture	Conchoidal
mohs	7
lustre	Vitreous
refractive	nω = 1.543–1.553
nε = 1.552–1.554
opticalprop	Unixal (+)
birefringence	+0.009
pleochroism	Amethyst section shows weak to moderate purple/reddish purple
"Citrine" section shows very weak yellow/orange
streak	white
gravity	2.65
melt	1650±75 °C
diagnostic	Distinct segments that are purple and yellow
solubility	Insoluble in common solvents
diaphaneity	Transparent to translucent
impurities	Iron

nε = 1.552–1.554 "Citrine" section shows very weak yellow/orange

Ametrine, also known as trystine, golden amethyst, or by the trade name bolivianite, is a variety of quartz with alternating zones of purple and yellow-orange coloration. Its name is a portmanteau of amethyst and citrine. While ametrine is commonly referred to as a combination of these two quartz varieties, some sources claim this is not accurate. Almost all commercially available ametrine is mined in Bolivia.

Color

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 of iron in the crystal structure. The difference in coloration is due to the iron existing in different oxidation 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 from aluminum-based color centers, similar to those of smoky quartz. This definition excludes any amethyst that has been oxidized by heat. Accordingly, the yellow quartz in ametrine would not be considered true citrine.

Origin

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

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.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

Structure

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

History

Legend has it that ametrine was first introduced to Europe by a conquistador's gifts to the Spanish Queen in the 1600s, after he received a mine in Bolivia as a dowry when he married a princess from the native Ayoreos tribe.

References

"Ametrine Value, Price, and Jewelry Information - International Gem Society". International Gem Society.
"Ametrine".
"Citrine".
"Quartz (var. ametrine) {{!}} Smithsonian National Museum of Natural History".
Vasconcelos, Paolo; Wenk, Hanz-Rudolf; Rossman, George. "The Anahí Ametrine Mine, Bolivia," Gems and Gemology, Spring 1994, p. 4-23

Info: Wikipedia Source

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