Crossword clue: a native sulphide of copper, occuring in masses of a dark blue color; -- hence called indigo copper.

The most common answer is covelline (9 letters).

2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

Possible answers

covelline 9 letters web-def

A native sulphide of copper, occuring in masses of a dark blue color; -- hence called indigo copper.

covellite 9 letters web-def

A native sulphide of copper, occuring in masses of a dark blue color; -- hence called indigo copper.