write a detail note on various types of rocks?
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Rock, in geology, naturally occurring and coherent aggregate of one or more minerals. Such aggregates constitute the basic unit of which the solid Earth is composed and typically form recognizable and mappable volumes. Rocks are commonly divided into three major classes according to the processes that resulted in their formation. These classes are (1) igneous rocks, which have solidified from molten material called magma; (2) sedimentary rocks, those consisting of fragments derived from preexisting rocks or of materials precipitated from solutions; and (3) metamorphic rocks, which have been derived from either igneous or sedimentary rocks under conditions that caused changes in mineralogical composition, texture, and internal structure. These three classes, in turn, are subdivided into numerous groups and types on the basis of various factors, the most important of which are chemical, mineralogical, and textural attributes.
Rocks can be any size. Some are smaller than these grains of sand. Others, like this large rock that was dropped as a glacier melted, are as large as, or larger than, small cars.
Rocks can be any size. Some are smaller than these grains of sand. Others, like this large rock that was dropped as a glacier melted, are as large as, or larger than, small cars.
Rock types
Learn how igneous, sedimentary, and metamorphic rock become one another in the rock cycle
Learn how igneous, sedimentary, and metamorphic rock become one another in the rock cycle
The Earth's surface and crust are constantly evolving through a process called the rock cycle.
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Igneous rocks are those that solidify from magma, a molten mixture of rock-forming minerals and usually volatiles such as gases and steam. Since their constituent minerals are crystallized from molten material, igneous rocks are formed at high temperatures. They originate from processes deep within the Earth—typically at depths of about 50 to 200 kilometres (30 to 120 miles)—in the mid- to lower-crust or in the upper mantle. Igneous rocks are subdivided into two categories: intrusive (emplaced in the crust), and extrusive (extruded onto the surface of the land or ocean bottom), in which case the cooling molten material is called lava.
(Bed) Rocks and (Flint) Stones
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Sedimentary rocks are those that are deposited and lithified (compacted and cemented together) at the Earth’s surface, with the assistance of running water, wind, ice, or living organisms. Most are deposited from the land surface to the bottoms of lakes, rivers, and oceans. Sedimentary rocks are generally stratified—i.e., they have layering. Layers may be distinguished by differences in colour, particle size, type of cement, or internal arrangement.
Metamorphic rocks are those formed by changes in preexisting rocks under the influence of high temperature, pressure, and chemically active solutions. The changes can be chemical (compositional) and physical (textural) in character. Metamorphic rocks are often formed by processes deep within the Earth that produce new minerals, textures, and crystal structures. The recrystallization that takes place does so essentially in the solid state, rather than by complete remelting, and can be aided by ductile deformation and the presence of interstitial fluids such as water. Metamorphism often produces apparent layering, or banding, because of the segregation of minerals into separate bands. Metamorphic processes can also occur at the Earth’s surface due to meteorite impact events and pyrometamorphism taking place near burning coal seams ignited by lightning strikes.
Geologic materials cycle through various forms. Sediments composed of weathered rock lithify to form sedimentary rock, which then becomes metamorphic rock under the pressure of Earth's crust. When tectonic forces thrust sedimentary and metamorphic rocks into the hot mantle, they may melt and be ejected as magma, which cools to form igneous, or magmatic, rock.
Geologic materials—mineral crystals and their host rock types—are cycled through various forms. The process depends on temperature, pressure, time, and changes in environmental conditions in the Earth’s crust and at its surface. The rock cycle illustrated in Figure 1 reflects the basic relationships among igneous, metamorphic, and sedimentary rocks. Erosion includes weathering (the physical and chemical breakdown of minerals) and transportation to a site of deposition. Diagenesis is, as previously explained, the process of forming sedimentary rock by compaction and natural cementation of grains, or crystallization from water or solutions, or recrystallization. The conversion of sediment to rock is termed lithification.
Explanation:
Density
rock type number of samples mode (grams per cubic cm)
all rocks 1,647 2.65
andesite 197 2.58
basalt 323 2.88
diorite 68 2.89
