Quartz and its colored varieties

� Quartz mine in Minas Gerais, Brazil

Iron-containing varieties:

Amethyst

Large geodes of amethyst occur in basalts in southern Brazil and northern Uraguay.

The color of amethyst is the result of radiation damage to Fe3+ in the interstitial site of quartz.� The radiation could be due to gamma rays from 40K.� Current theory says that the ferric iron is oxidized to Fe4+ by the gamma rays.


Amethyst geodes in basalt near the town of Ametista do Sul, Rio Grande do Sul, Brazil
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Amethyst geodes and citrine geodes (heated amethyst ) for sale near Rio de Janerio, Brazil.

Amethyst geode from Rio Grande do Sul, Brazil

Citrine

Most citrine is made by heating amethyst.� Typically low-quality amethyst is heated to develop the citrine color.
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Synthetic Russian citrine is produced directly by the addition of iron to the growth solutions.� It owes its color to Fe3+ clusters in the quartz.

Green quartz

One of the rarities of nature, green quartz forms when amethyst from certain deposits is heated to a critical temperature.� The color is from Fe2+ in the approximately octahedral interstitial site.� Green quartz can be made synthetically by adding Be2+ to the tetrahedral site which allows more Fe2+ into the interstitial site from the coupled substitution:� Si4+ (td) = Be2+ (td) + Fe2+ (int).

Here is natural green quartz which resulted from an amethyst deposit being overrun by a basalt flow.� This is from Thunder Bay, Canada. Specimen provided by SA Kissin.
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Synthetic green quartz with Fe2+ in the interstitial site.

Ametrine

Ametrineis bi-colored variety of quartz containing both amethyst and citrine zones
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�This slice and crystal are from the only significant source in the world, the Anah� Mine, Bolivia.
Much more information on ametrine can be found at this link.

Smoky quartz

�The result of radiation damage to Al-containing quartz.

The crystal on the left looked like the one on the right before it was exposed to about 10 Megarads of gamma radiation from 137Cs.
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Rose quartz (common, massive rose quartz)

Click here for more information on rose quartz. The color of common, massive rose quartz is from sub-microscopic fibers of a phase related to dumortierite.
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Asterism (star reflection of light) in rose quartz.� The reflection comes from the fibers which are partially ordered along the a-axes of the quartz.� Photo courtesy of M Scott A scanning electron microscope image of the fibers extracted from rose quartz.� The individual fibers are about 0.1 mm wide.� The false color in the image is close to the true color of the fibers. SEM photo courtesy of J Goreva, Caltech.

Rose quartz (uncommon, crystalline rose quartz)

There is an rare type of rose quartz (also called pink quartz) which differs from the abundant massive rose quartz found throughout the world.� It is found in veins up to about 6 cm wide of rose colored euhedral crystals.� This material occurs in phosphate pegmatites near Galil�ia (near Gov. Valadares), Minas Gerais, and a few other localities in Brazil.� It is photosensitive; the color of the natural crystals fades in light and can be regenerated by exposing the crystals to ionizing radiation. The color mechanism has been proven in the synthetic material.� It is synthesized by growing quartz in the presence of aluminum and phosphate, and exposing the product to gamma rays.
Al - O2- - P�� +� g-ray�� ����� Al - O- - P��� +�� electron

Rose quartz crystals from Minas Gerais, Brazil.�
Picture courtesy of S. Pitts

A slab of synthetic Russian rose quartz grown with Al and P substitutions and subsequently irradiated with gamma rays to develop the deep rose color.�
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Specimen courtesy of V Balitsky

Blue quartz

Natural blue quartz contains sub-microscopic inclusions of ilmenite or larger inclusions of other phases.
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These are inclusions in 'blue quartz' from Madagascar.� The ~0.1 mm inclusions are probably in the lazulite-scorzalite series. This blue-grey quartz from Nelson, Virginia, contains micro inclusions of ilmenite. TEM photo courtesy of Ma Chi, Caltech

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Chrysoprase

The color of chrysoprase is due to minute inclusions (98K) of nickel silicates in the silica. In the case of the Australian chrysoprase, the nickel silicate is a member of the talc group which been identified both as willemseite, (Ni,Mg)3Si4O10(OH)2, and as kerolite, a variety of talc with a randomly stacked structure, in the series, kerolite - nickel-kerolite.

Colorless quartz

�Colorless, synthetic quartz grown by the Western Electric Corporation for use in communication devices.
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A large group of colorless quartz crystals from Hot Springs, Arkansas.�
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Picture courtesy of Jewel Tunnel Imports.

Agate

� This agate slice is from Rio Grande do Sul, Brazil.� The agates occur in the same basalts as the amethyst geodes.� This is a slice in its natural state.� Many agates are dyed or treated to change their colors.

Fluid Inclusions

This is a smoky quartz crystal from Minas Gerais, Brazil, with a large
fluid inclusion (water) with a large gas bubble above the water.
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