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Ch. 13: Olivine - Sphene

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276                               PRECIOUS STONES.
with rocks that have been subjected to dynamo- (and in many cases thermo-) metamorpbism. Consistent with this we find the mineral often shows flaws or " feathers," though in other respects it is remarkably free from imperfection. The pink variety is very frequently flawed in this way (Fig. 40).
It is often found associated with Quartz, Albite, Lepidolite,
Beryl, Idocrase, Garnet, Spinel, Cassiterite, Talc, Eutile, Chrysoberyl, etc.
The varieties are mostly classified according to colour. The common black type is known as Schorl; a black variety from Kragero in Norway is known as Aphrizite. The red colours are comprised under Rubellite, the violet-red speci­mens from Siberia being called Siberite. Rubellite has a specific gravity of 3"08. Indicolite (or Indigolite) includes the blue shades (density 3-16), the deeper Berlin-blue crystals from Brazil being called Brazilian Sapphire. The
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