A mineral or substance related to silk or silkworm products, though this term is extremely rare in modern usage.
From 'bombic' (relating to silk from Greek 'bombyx') plus the mineral suffix '-cite.' This appears to be a 19th-century mineral naming convention that never became standard.
This word is so obscure that it might appear in only a handful of ancient mineralogy textbooks—it's the kind of term that shows how scientists used to name things based on where they came from rather than what they really were.
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