The Anahí mine,
Bolivia, has produced large amounts of
amethyst, citrine, and
amethyst-citrine for the gem market. Field and experimental
investigations conclusively show that the amethyst-citrine color
combination in quartz crystals from Anahí is natural and
does not result from laboratory treatment. The unusual color patterns
probably result from the uncommon geologic conditions under which these
quartz crystals formed, although the crystal chemical properties
constrolling the sector color zoning still elude explaination. From
1989 to the present, more than 100 tons of ametrine crystals, yielding
40-80 kb of cutting rough per ton, have been produced.
Gems & Gemology (1994)