Knowra Hornblende Hornblende Hornblende is a dark, commonly black or green amphibole mineral found in igneous and metamorphic rocks. Its complex composition varies, but its crystal structure contains double chains of silicate tetrahedra.
Amphibole : A group of silicate minerals characterized by double-chain structures and commonly elongated crystals. Hornblende is a major amphibole mineral, sharing the group’s characteristic structure.
Crystal structure : The ordered, repeating arrangement of atoms in a crystalline solid. Hornblende’s double-chain arrangement determines its characteristic cleavage directions.
Petrography : The systematic description and classification of rocks, especially through microscopy. Petrographers identify hornblende by its optical properties, shape, and cleavage.
Augite : A common calcium-rich pyroxene mineral, usually dark green to black, with nearly right-angle cleavage. Augite resembles hornblende but has pyroxene cleavage angles near 90°.
Silicate mineral : A mineral built primarily from silicon–oxygen tetrahedra, alone or linked into larger structures. Hornblende’s framework is made from linked silicon–oxygen tetrahedra.
Cleavage (crystal) : The tendency of a mineral to break along planes of weak bonding in its crystal structure. Hornblende commonly cleaves along two directions meeting at about 56° and 124°.
Thin section : A slice of rock ground thin enough for light to pass through under a microscope. Thin sections reveal hornblende’s pleochroism and distinctive amphibole cleavage.
Biotite : A dark mica mineral that splits readily into thin, flexible sheets. Biotite is another dark rock-forming mineral, distinguished by its sheet-like cleavage.
Inosilicate : A silicate mineral whose tetrahedra form chains, either single or double. Hornblende belongs to the double-chain inosilicates.
Mohs scale : A qualitative scale that ranks minerals by their resistance to scratching. Hornblende’s hardness of roughly 5–6 helps distinguish it from softer dark minerals.
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