Minerals / Tourmaline, rossmanite var.

Tourmaline is a boron silicate mineral, which occurs as an accessory mineral in igneous and metamorphic rocks. There are a large number of varieties of tourmaline, each with a slightly different composition, resulting in a wide range of colours. Rossmanite has the formula  (LiAl₂)Al₆Si₆O₁₈ (BO₃)₃(OH)₃OH  and is  is usually described as being pink in colour, however, this specimen from Cornwall  has a grey green colour, and is composed of tightly compacted radiating sprays of prismatic crystals.

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