glaucophane

Century Dictionary and Cyclopedia

1. n. A bluish or bluish-black mineral belonging to the amphibole or hornblende family, containing 7 per cent, of soda. It is a characteristic constituent of certain crystalline schists.

Wiktionary

1. n. mineralogy A mixed aluminate of sodium, magnesium and aluminium that has a characteristic blue colour, and exhibits pleochroism, with the chemical formula Na2(Mg,Fe2+)3Al2Si8O22(OH)2.

GNU Webster's 1913

1. n. (Min.) A mineral of a dark bluish color, related to amphibole. It is characteristic of certain crystalline rocks.