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64 A Book of Precious Stones
vertically. The specific gravity of the trans-parent flawless beryl is 2.73., usually 2.69 to
2.70;
hardness, 7.5 to 8; brittle; cleavage indistinct; fracture uneven to
conchoidal; lustre vitreous, sometimes resinous. Beryl colours include
emerald green to pale green, pale blue, pale yellow, honey, wine and
citriue yel-low, white, and pale rose-red. Pleochrism is unusually
distinct, sometimes strong, in the emerald especially, which through
the dichroi-scope reveals two different shades of green.
Beryl includes the emerald, aquamarine, go-shenite, and davidsonite. The differences are principally in colour.
Beryl
is a silicate of the metals aluminium and beryllium, containing the
oxide alumina in small amount, which is, however, a more important
constituent in corundum, spinel, and chrysoberyl. There is some
variation in beryl from different localities; the chemist Lewy, who
analysed the beautiful emerald beryl that is found at Muzo in Colombia,
South America, found: silica, 67.85; alumina, 17.95; beryllia, 12.4;
magnesia, 0.9; soda, .07; water, 1.66; and organic matter 0.12, besides
a trace of chromic oxide. An analysis of a specimen of aquamarine from
Adun-Chalon in Siberia by Penfield
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