What are 3 characteristics of pegmatite?
pegmatite Very coarse-grained, igneous rock, usually of granitic composition, in which the individual crystals are at least 2.5 cm long. The crystals are often more than 1 m in length, and may be far larger. Crystallization occurs at a late stage, when the magma is enriched in volatiles and trace elements.
Does pegmatite have pyroxene?
Rarer intermediate composition and mafic pegmatites containing amphibole, Ca-plagioclase feldspar, pyroxene, feldspathoids and other unusual minerals are known, found in recrystallised zones and apophyses associated with large layered intrusions. The product of pegmatite decomposition is euclase.
What temperature does pegmatite form?
In short, we argue that pegmatite formation in the Smartville gabbros, and probably many other gabbroic plutons, reflects water saturation of a magma at high temperature, estimated here at >900°C.
What is the definition of pegmatites?
Definition of pegmatite : a coarse variety of granite occurring in dikes or veins.
How do pegmatites form?
The extreme conditions of crystallization sometimes produce crystals that are several meters in length and weigh over one ton. Pegmatites form from waters that separate from a magma in the late stages of crystallization; this activity often occurs in small pockets along the margins of a batholith.
Which igneous rock is aphanitic?
basalt
Examples of aphanitic igneous rock include basalt, andesite and rhyolite. Glassy or vitreous textures occur during some volcanic eruptions when the lava is quenched so rapidly that crystallization cannot occur. The result is a natural amorphous glass with few or no crystals. Examples include obsidian.
What is another term for Phaneritic?
term for small crystals, and phaneritic for larger ones. Very coarse crystals (those larger than 3 centimetres, or 1.2 inches) are termed pegmatitic. aid of a microscope (called phaneritic, from the Greek phaneros, meaning “visible”).
What is Phaneritic and aphanitic?
APHANITIC TEXTURE – Igneous rocks that form on the earth’s surface have very fine-grained texture because the crystals are too small to see without magnification. PHANERITIC TEXTURE – Igneous rocks with large, visible crystals because the rock formed slowly in an underground magma chamber.