Grovacca
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A greywacke hand specimen from the GeoDIL rock collection. Source
Description
Greywacke, also written graywacke, is sandstone containing a mixture of mineral and rock fragments in a finer matrix. It is commonly grey to black and may contain pale quartz veins. Deformation and jointing can give individual blocks a strongly marked structure.
History
Greywacke begins as deposited sediment that is compacted and cemented into rock. Later geological movement can fold, fracture and vein it. These changes remain visible in stone selected for sculpture or landscape work.
Commissioning
The carver should assess the proposed block before the final form is fixed. Veins may contribute to the composition, while joints can limit the usable stone. The intended face, finish and support are best considered during selection.