An introduction to igneous rocks requires exploration of three core ideas. Slow cooling plus high water content. The environment of formation produces characteristic textures in igneous rocks which aid in their identification.
The rate of cooling of the magma is slow, allowing large crystals to grow. Crystal size primarily reflects the rate of cooling, but is also often strongly affected by rock composition especially water or gas content.
Slow cooling plus high water content Glassy: Other features The chemical composition of the magma determines which minerals will form and in what proportions they will occur.
Rapid cooling from a lava flow is not. Fast cooling Porphyritic with coarse-grained groundmass: This type of rocks are also referred as plutonic or intrusive.
Fine grained aphanitic: Igneous rock texture indicates the rate of magmatic cooling. For example, the silica-rich extrusive rock, rhyolite , common in continental volcanic regions, is the fine-grained equivalent of intrusive granite.
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Fichtels jmu. Igneous rocks form by crystallization of minerals from liquid magma rising into the upper portion of Earth 's crust from the lower crust and underlying mantle. Granite and basalt are the two most abundant igneous rocks at the earth's surface.
Igneous rocks are therefore classified as either intrusive plutonic or extrusive volcanic. Igneous Textures Geologists like igneous textures because they reveal so much about how a rock formed. The flattened pumice clasts are lenticular lens-shaped in cross-section and are called fiamme Italian for flame. This texture is exhibited by some volcanic rocks.