Amethyst
Purple coarse crystalline Quartz is called Amethyst. It is cherished as a gem, lapidary
material, ornamental rock, and for mineral specimens. Most Amethyst was formed by
hydrothermal processes (deposited by water at comparatively low temperatures) in voids
in basalt (volcanic rock). The gorgeous Brasilian druses line vugs in basalt, that may be
as much as two meter long, and the intricate prismatic crystals from 'Brandberg' in
Namibia grow individually in basalt vugs as well.
There is some dispute about the origin of colour in Amethyst, but it seems to be due at
least in part to iron in colour centers. When heated, Amethyst changes colour, first it
turns brown and becomes 'Citrine', subsequently it looses colour and turns grey or
white. The transformation is not reversible.
Yellow to golden brown, coarse crystalline Quartz is called Citrine. Virtually all
commercially available Citrine is produced by heat treatment of Amethyst. The only
prominent exception from this is the Bolivian 'Ametrine', that is naturally occurring
intergrown Amethyst and Citrine.
Specimen Handling
Amethyst is for all practical purposes stable in a normal household environment. It is
not harmed by light, changes in temperature in the normal comfort range, or known to
decompose. Amethyst specimens can be fragile and should be handled with care like any
other mineral specimen. Quartz is not appreciably soluble in water. But ... many
Amethyst crystals contain voids filled with water and gas, as do so-called 'enhydros',
Agate geodes enclosing a large cavity filled by air and water, and you may believe it is
'sealed in,' but take my word for it, it isn't. Water vapor easily passes through Quartz.
Such specimens may also be susceptible to damage if exposed to high temperatures or
sun light. Keep them in the shade, and don't cry when the water is gone. Some Amethyst
is susceptible to fade, when exposed to sun light. The rule of thumb is, all Amethyst
fades, but most of it fades slowly.
A specimen of synthetic Amethyst, produced in Russia.
Bibliography
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This page is authored by Claus Hedegaard.
