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Rhyodacite is an extrusive volcanic rock intermediate in composition between dacite and rhyolite
Rhyo lite + dacite : a rock intermediate between rhyolite and dacite that is the extrusive equivalent of granodiorite
Durable Rock, Medium Hardness Rock
Fine Grained Rock, Opaque Rock
Picrite is a variety of high-magnesium olivine basalt that is very rich in the mineral olivine
From Greek pikros bitter + -ite, 19th century
Fine Grained Rock, Opaque Rock