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The black tourmaline is called “Schorl”. The mineral shown in this photo is longitudinally grown into a feldspar (orthoclas). It has vertical striations in parallel with the main axis. The mineral
comes from Brasil.
Chemically it is a iron and bor- rich cyclosilicate with a Mohs hardness of about 7. It is not fissionable and its break is brittle
The crystals are ditrigonal, triangular in diameter and roundish sides.
This mineral is a twin; the bigger crystal is 12 cm long, the other 8 cm.
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