Everything about Shale totally explained
Shale (also called
mudstone) is a fine-grained
sedimentary rock whose original constituents were
clay minerals or
muds. It is characterized by thin laminae breaking with an irregular curving fracture, often splintery and usually parallel to the often-indistinguishable bedding plane. This property is called
fissility. Non-fissile
rocks of similar composition but made of particles smaller than 1/16 mm are described as
mudstones. Rocks with similar particle sizes but with less clay and therefore grittier are
siltstones. Shale is the most common sedimentary rock.
Formation
The process in the
rock cycle which forms shale is
compaction. The fine particles that compose shale can remain in water long after the larger and denser particles of sand have deposited. Shales are typically deposited in very slow moving water and are often found in lake and
lagoonal deposits, in
river deltas, on
floodplains and offshore of beach sands. They can also be deposited on the
continental shelf, in relatively deep, quiet water.
'Black shales' are dark, as a result of being especially rich in
unoxidized carbon. Common in some
Paleozoic and
Mesozoic strata, black shales were deposited in
anoxic,
reducing environments, such as in stagnant water columns.
Fossils, animal tracks/burrows and even raindrop impact craters are sometimes preserved on shale bedding surfaces. Shales may also contain
concretions.
Shales that are subject to heat and pressure alter into a hard, fissile,
metamorphic rock known as
slate, which is often used in building construction.
Further Information
Get more info on 'Shale'.
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