Crossword clue: a white variety of amphibole, or hornblende, occurring in long, bladelike crystals, and coarsely fibrous masses.
1 answer found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).
Possible answers
a white or pale green mineral (calcium magnesium silicate) of the amphibole group used as a form of asbestos