[mass noun] A typically black or blackish mineral that occurs as prismatic crystals in granitic and other rocks. It consists of a boron aluminosilicate and has pyroelectric and piezoelectric properties.
- ‘It consists of clasts of angular to rounded quartz, plagioclase, tourmaline and rock fragments, up to 3 mm in diameter.’
- ‘The mineral assemblage comprises quartz, K-feldspar, albitic plagioclase, white mica, apatite, tourmaline and garnet.’
- ‘Inclusions of quartz, tourmaline, apatite, and muscovite crystals have been described.’
- ‘After quartz and microcline, tourmaline is arguably the next most abundant mineral found in the miarolitic cavities.’
- ‘In the line rock, this black tourmaline occurs as tiny prismatic crystals.’
Mid 18th century: from French, based on Sinhalese tōramalli carnelian.