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VESUVIANITE
(IDOCRASE)
This mineral affords transparent stones of pale brown, green, or yel­low colors, which closely resemble in appearance cut gems of smoky quartz, tourmaline, chrysolite, hyacinth, or essonite. They have a rich luster due to a combination of resinous and vitreous characters, and are sufficiently dichroic to be of interest from that point of view. Nearly all the cut stones come from the occurrence at Mount Vesuvius (whence the mineral obtains its name), or from one on the Mussa Alp, in the Ala valley of the Piedmont plateau, Italy. The crystals from Vesuvius are generally brownish to colorless, while those of the Pied­mont are green.
The hardness of vesuvianite is 6.5, sufficient to give it a fair wear­ing quality. Its specific gravity is 3.35 to 3.45. In composition it is a complex silicate, chiefly of aluminum and calcium. It is fusible before the blowpipe. It has a strong tendency to crystallize, the crystals belonging to the tetragonal system, and usually appearing essentially as short, stout prisms.
It is not an uncommon mineral, but is usually too opaque to make desirable gems. Its occurrence is especially associated with limestone, either as the result of metamorphism or direct volcanic eruption, as at Vesuvius. A yellowish brown variety, known as xanthite, occurs at Amity, New York, and an occurrence on the Vilui River, near Lake Baikal, Siberia, is known as viluite.
The cut stones are made exclusively from clear crystals, which rarely afford stones exceeding a few carats in size. The step or table cut is the form usually given the stones.
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