What is phenocryst texture?
Definition. A phenocryst is visible large crystal embedded within a fine-grained matrix of smaller crystals. This combination of matrix and phenocrysts forms a porphyritic rock texture.
What is a pyroclastic texture?
A pyroclastic texture shows a mixture of rock fragments, pumice, and volcanic ash. The ash is very fine grained, so only the rock fragments and pumice are identifiable.
What is interstitial texture?
Ophitic texture, a variant the poikilitic texture, is one where random plagioclase laths are enclosed by pyroxene or olivine. If plagioclase is larger and encloses the ferromagnesian minerals, then the texture is subophitic and the laths typically impinge on one another to form sharp angles.
What is the meaning of porphyritic texture?
A porphyritic texture displays minerals in two distinct size populations: one or more minerals are consistently larger than the rest of the minerals in a rock. The extra large mineral grains are called phenocrysts.
What is a phenocryst phase?
Phenocrysts are free-growth (unimpeded) forms that have developed while supported by a fluid phase. Slowly grown crystals tend to be more nearly perfect, whereas rapidly grown crystals contain twins, zoning, mosaic structure, and inclusions of solid, liquid, or gas phases.
What is a phenocryst quizlet?
A phenocryst is a relatively large and usually conspicuous crystal distinctly larger than the grains of the rock groundmass of an igneous rock. Such rocks that have a distinct difference in the size of the crystals are called porphyries, and the adjective porphyritic is used to describe them.
What is the texture of rhyolite?
Rhyolite
| Type | Igneous Rock |
|---|---|
| Texture | Aphanitic (Fine-grained) |
| Origin | Extrusive/Volcanic |
| Chemical Composition | Felsic |
| Color | Light Gray |
What is exsolution texture?
Exsolution texture, a general term for the texture of mineral intergrowth formed by solid exsolution, is a common texture in minerals from both magmatic and metamorphic rocks. This texture is important for understanding variations of metamorphic conditions.
What is Granoblastic texture?
Granoblastic is an adjective describing an anhedral phaneritic equi-granular metamorphic rock texture. Granoblastic texture is typical of quartzite, marble, charnockites and other non-foliated metamorphic rocks without porphyroblasts.
How does a porphyritic texture form?
A porphyritic texture is developed when magma that has been slowly cooling and crystallising within the Earth’s crust is suddenly erupted at the surface, causing the remaining uncrystallised magma to cool rapidly. This texture is characteristic of most volcanic rocks.