Editing Greywacke (section)

{{Short description|Sandstone with angular grains in a clay-fine matrix}}

[[File:Greywacke-f-and-l.jpg|thumb|right|Photomicrographs of feldspathic (L) and lithic (R) greywacke. The top images are in [[Plane polarized light|plane-polarized light]]; the bottom images are in [[cross-polarized light]]. Cements fill the pore spaces.]]
[[File:Menkaura Bust Closeup.jpg|thumb|Closeup of Pharaoh [[Menkaure]]'s greywacke statue, 25th century BCE, from the [[Egyptian Museum]] in [[Cairo]]]]

'''Greywacke''' or '''graywacke''' ({{langx|de|Grauwacke}} {{gloss|a grey, earthy rock}}) is a variety of [[sandstone]] generally characterized by its [[hardness]] (6–7 on [[Mohs scale]]), dark color, and [[Sorting (sediment)|poorly sorted]] angular grains of [[quartz]], [[feldspar]], and small rock fragments or sand-size [[Lithic fragment (geology)|lithic fragments]] set in a compact, [[clay]]-fine matrix. It is a texturally immature [[sedimentary rock]] generally found in [[Paleozoic]] [[Stratum|strata]]. The larger [[Particle size (grain size)|grain]]s can be sand- to gravel-sized, and [[Matrix (geology)|matrix]] materials generally constitute more than 15% of the rock by volume.