Generic garnets

Article Abstract:

Mineralogists define garnets as cubic crystal silicates and classify them according to their mineral content. These are pyrope, almandine, spessartine, uvarovite, grossular and andradite. Also rated as possessing gem quality are such hybrids as rhodolite, hessonite and 'malaya.' There are varieties outside the six groups, but they are not considered significant.

Author: Pough, Frederick H.
Composition, Silicate minerals, Garnet

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Pollucite & petalite

Article Abstract:

Pollucite and petalite are two of the rarest gemstones that interest every dedicated collector. Pollucites, which were first found on the Mediterranean island of Elba, can be found in Maine and in the Connecticut pegmatite belt. Colorless pollucite crystals, meanwhile, are found in Afghanistan.

Author: Pough, Frederick H.
Afghanistan, Maine, Natural resources, Elba

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Sillimanite

Article Abstract:

Sillimanite is an uncommon gem named for 19th-century Yale mineralogy professor Benjamin Silliman. Its structure, formation and sources are described.

Author: Pough, Frederick H.
Gems

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Subjects list: Varieties, Precious stones
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