Definition
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Etymology
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Tachylite is a vitreous form of basaltic volcanic glass. This glass is formed naturally by the rapid cooling of molten basalt
From German Tachylite, from tachy- + Greek lutos soluble, melting
Durable Rock, Medium Hardness Rock
Coarse Grained Rock, Fine Grained Rock, Medium Grained Rock, Opaque Rock
Greywacke is defined as a dark coarse-grained sandstone rock which contains more than 15 per cent clay
From German Grauwacke, from grau grey + wacke
Fine Grained Rock, Opaque Rock