Definition
Greywacke is defined as a dark coarse-grained sandstone rock which contains more than 15 per cent clay
Chalk is a soft, white, powdery limestone consisting mainly of fossil shells of foraminifers
History
Origin
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Discoverer
Unknown
Unknown
Etymology
From German Grauwacke, from grau grey + wacke
From old English cealc chalk, lime, plaster; pebble, from Greek khalix small pebble, in English transferred to the opaque, white, soft limestone
Class
Sedimentary Rocks
Sedimentary Rocks
Sub-Class
Durable Rock, Hard Rock
Durable Rock, Soft Rock
Family
Group
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Other Categories
Fine Grained Rock, Opaque Rock
Fine Grained Rock, Opaque Rock