Everything about Rock Geology totally explained
In
geology,
rock is a
naturally occurring aggregate of
minerals and/or
mineraloids. The Earth's
lithosphere is made of rock. In general rocks are of three types, namely,
igneous,
sedimentary, and
metamorphic.
Petrology is the scientific study of rocks.
Rock classification
Rocks are classified by mineral and
chemical composition, by the
texture of the constituent particles and by the processes that formed them. These indicators separate rocks into
igneous,
sedimentary and
metamorphic. They may also be classified according to
particle size, in the case of
conglomerates and
breccias or in the case of individual
stones. The transformation of one rock type to another is described by the geological model called the
rock cycle.
Igneous rocks are formed when molten
magma cools and are divided into two main categories:
plutonic rock and
volcanic. Plutonic or intrusive rocks result when magma cools and crystallizes slowly within the
Earth's crust (example
granite), while volcanic or extrusive rocks result from magma reaching the surface either as
lava or fragmental ejecta (examples
pumice and
basalt) .
Sedimentary rocks are formed by deposition of either
clastic sediments, organic matter, or chemical precipitates (
evaporites), followed by compaction of the particulate matter and cementation during
diagenesis. Sedimentary rocks form at or near the Earth's surface. Mud rocks comprise 65% (
mudstone,
shale and
siltstone);
sandstones 20 to 25% and
carbonate rocks 10 to 15% (
limestone and
dolostone).
Coloration
Iron oxides and
carbonates play a large part in many sedimentary rocks and are especially important as coloring agents. The red sands and limestones, for example, which are so abundant, contain small amounts of
iron(III) oxide (
hematite), which in a finely divided state gives a red hue to all rocks in which it's present.
Limonite and
goethite, on the other hand, makes rocks yellow or brown;
manganese oxides,
asphalt and other
carbonaceous substances are the cause of the black color of many sediments. Bluish tints result sometimes from the presence of
phosphates or of
fluorite; while green is most frequently seen in rocks which contain
glauconite or
chlorite.
Impact on society
Rocks have had a huge impact on the cultural and technological advancement of the human race. Rocks have been used by
Homo sapiens and other
hominids for millions of years.
Lithic technology marks some of the oldest and continuously used technologies. The
mining of rocks for their
metal ore content has been one of the most important factors of human advancement. Humanity's advancement has been decided by the kind of metals available from the rocks of a region. The prehistory and early history of civilization is classified into the
stone age,
Bronze Age, and
Iron Age. Rocks have been and continue to be used to construct buildings and
infrastructure. When so used, they're
dimension stone.
Further Information
Get more info on 'Rock Geology'.
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