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Igneous textures include the rock textures occurring in igneous rocks. Igneous textures are used by geologists in determining the mode of origin of igneous rocks and are used in rock classification. The six main types of textures are phaneritic, aphanitic, porphyritic, glassy, pyroclastic, and pegmatitic.
It is generally glassy or fine-grained in texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral assemblage is predominantly quartz, sanidine, and plagioclase. It is the extrusive equivalent of granite.
A chilled margin is a shallow intrusive or volcanic rock texture characterised by a glassy or fine-grained zone along the margin where the magma or lava has contacted air, water, or particularly much cooler rock. This is caused by rapid solidification of the melt near the contact with the surrounding low temperature environment.
In geology, texture or rock microstructure [1] refers to the relationship between the materials of which a rock is composed. [2] The broadest textural classes are crystalline (in which the components are intergrown and interlocking crystals), fragmental (in which there is an accumulation of fragments by some physical process), aphanitic (in which crystals are not visible to the unaided eye ...
Vesicular texture is a volcanic rock texture characterized by a rock being pitted with many cavities (known as vesicles) at its surface and inside. [ 1 ] This texture is common in aphanitic , or glassy, igneous rocks that have come to the surface of the Earth, a process known as extrusion .
Volcanic rocks are usually fine-grained or aphanitic to glass in texture. They often contain clasts of other rocks and phenocrysts. Phenocrysts are crystals that are larger than the matrix and are identifiable with the unaided eye. Rhomb porphyry is an example with large rhomb shaped phenocrysts embedded in a very fine grained matrix.
Vitreous minerals have the lustre of glass. (The term is derived from the Latin for glass, vitrum.) This type of lustre is one of the most commonly seen, [9] and occurs in transparent or translucent minerals with relatively low refractive indices. [2] Common examples include calcite, quartz, topaz, beryl, tourmaline and fluorite, among others.
Most scoria is composed of glassy fragments and may contain phenocrysts. A sample from Yemen was mainly composed of volcanic glass with a few zeolites (e.g., clinoptilolite). [3] The geological term cinder is synonymous and interchangeable with scoria, though scoria is preferred in scientific literature.