arf·ved·son·ite
| \ ˈävə̇dsəˌnīt \
plural -s
Definition of arfvedsonite
: a silicate of sodium, calcium, and iron, approximately Na2–3(Fe, Mg, Al)5Si8O22(OH)2, of the amphibole group occurring in black monoclinic strongly pleochroic prisms in certain igneous rocks
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Merriam-Webster unabridged
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