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Grain size in igneous rocks results from cooling time so porphyritic rocks are created when the magma has two distinct phases of cooling. [18] Igneous rocks are classified on the basis of texture and composition. Texture refers to the size, shape, and arrangement of the mineral grains or crystals of which the rock is composed. [citation needed]
A chemical analysis is usually sufficient to indicate whether a rock is igneous or sedimentary, and in either case to accurately show what subdivision of these classes it belongs to. In the case of metamorphic rocks it often establishes whether the original mass was a sediment or of volcanic origin. [1]
Trachyte – Extrusive igneous rock – A silica-undersaturated volcanic rock; essentially a feldspathoid-bearing rhyolite; Troctolite – Igneous rock – A plutonic ultramafic rock containing olivine, pyroxene and plagioclase; Trondhjemite – Light-colored intrusive igneous rock – A form of tonalite where plagioclase-group feldspar is ...
In metamorphic rocks that experience deformation during metamorphism, porphyroblasts may grow before, during, or after the phase of deformation recorded by the matrix minerals. The relationship of porphyroblast growth to deformation is typically evaluated by comparing the shape orientation of trails of mineral inclusions in the porphyroblast to ...
Pumice is an igneous rock with a foamy appearance. The name is derived from the Latin word pumex (meaning "pumice") [13] which is related to the Latin word spuma meaning "foam". [14] In former times, pumice was called "Spuma Maris", meaning "froth of the sea" in Latin because the frothy material was thought to be hardened sea foam.
Metamorphic rocks are formed by subjecting any rock type—sedimentary rock, igneous rock or another older metamorphic rock—to different temperature and pressure conditions than those in which the original rock was formed. This process is called metamorphism, meaning to "change in form". The result is a profound change in physical properties ...
These rocks are fine-grained and sometimes cool so rapidly that no crystals can form and result in a natural glass, such as obsidian, however the most common fine-grained rock would be known as basalt. Any of the three main types of rocks (igneous, sedimentary, and metamorphic rocks) can melt into magma and cool into igneous rocks. [2]
Basic types of intrusions: 1. Laccolith 2. Small dike 3. Batholith 4. Dike 5. Sill 6. Volcanic neck, pipe 7. Lopolith As a general rule, in contrast to the smoldering volcanic vent in the figure, these names refer to the fully cooled and usually millions-of-years-old rock formations, which are the result of the underground magmatic activity shown.