Tourmaline

Tourmaline forms long prismatic crystals, often striated vertically. There are, however, also specimens in compact aggregates and in fibrous-radiating masses. The colour varies according to the chemical composition: multicoloured (elbaite), black (schorl), brown (dravite), pink (rubellite), blue (indicolite), colourless (achroite), etc. It is a very hard, heavy, insoluble mineral, with a fusibility that varies according to the quantities of iron and magnesium (the darker it is, the more difficult it will be to melt).

They form in granitic and pegmatitic rocks, but also in some eruptive and metamorphic rocks. It is often found associated with various minerals such as beryl, zircon, quartz and feldspar.

Specimens with intense colours and strong transparency are mostly used in gemmology, others are used by industry to exploit their piezoelectric properties.