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Greywacke or graywacke (German grauwacke, signifying a grey, earthy rock) is a variety of sandstone generally characterized by its hardness (6–7 on Mohs scale), dark color, and poorly sorted angular grains of quartz, feldspar, and small rock fragments or sand-size lithic fragments set in a compact, clay-fine matrix.
Ermelo Sandstone, Mpumalanga province, near der Farm de Roodepoort Matatiele Sandstone , KwaZulu-Natal province, near Matatiele Naboomspruit (also Golden Dawn or Golden Stone ) Limpopo province, around Warmbaths
Lithic sandstones can have a speckled (salt and pepper) or gray color, and are usually associated with one specific type of lithic fragment (i.e., igneous, sedimentary, or metamorphic). [ 1 ] Tectonically, lithic sandstones often form in a wide variety sedimentary depositional environments (including fluvial , deltaic , and alluvial sediments ...
Quartzite – Hard, non-foliated metamorphic rock – A metamorphosed sandstone typically composed of >95% quartz Schist – Easily split medium-grained metamorphic rock Semipelite – Metamorphic rock Pages displaying short descriptions of redirect targets – that falls between pelitic (clay-rich) and psammitic (sand-rich) compositions
The grey and white crystals are quartz and (limited) feldspar. Metamorphism is the transformation of existing rock (the protolith ) to rock with a different mineral composition or texture . Metamorphism takes place at temperatures in excess of 150 °C (300 °F), and often also at elevated pressure or in the presence of chemically active fluids ...
The Franciscan Complex is an assemblage of metamorphosed and deformed rocks, associated with east-dipping subduction zone at the western coast of North America. [6] Although most of the Franciscan is Early/Late Jurassic through Cretaceous in age (150-66 Ma), [ 7 ] some Franciscan rocks are as old as early Jurassic (180-190 Ma) age and as young ...
Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock ( protolith ) is subjected to temperatures greater than 150 to 200 °C (300 to 400 °F) and, often, elevated pressure of 100 megapascals (1,000 bar ) or more, causing profound physical or chemical changes.
The Bedford Shale of Michigan is a light gray [13] [14] or bluish-light gray in color. [15] [b] It is a silty shale, [15] siltier and sandier in its upper part. [14] The boundary with the Berea Sandstone exhibits thin veins ("stringers") of sandstone, indicating erosion of the Bedford Shale which was filled in later by sand. [17]