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Ignimbrite is a volcanic rock consisting mainly of pumice fragments, formed by the consolidation of material deposited by pyroclastic flows
From Latin ignis fire + imber, imbr- shower of rain, storm cloud + -ite
Durable Rock, Medium Hardness Rock
Fine Grained Rock, Opaque Rock
Gneiss is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from pre-existing formations that were originally either igneous or sedimentary rocks
From the Middle High German verb gneist (to spark; so called because the rock glitters)
Coarse Grained Rock, Medium Grained Rock, Opaque Rock