What type of rock is Oligoclase?

What type of rock is Oligoclase?

Oligoclase is a common mineral in the more silica-rich varieties of igneous rock and in many metamorphic rocks.

What is the chemical formula for a mid range composition of Oligoclase?

Oligoclase Mineral Data

Is anorthosite felsic or mafic?

Anorthosite /ænˈɔr/ is a phaneritic, intrusive igneous rock characterized by a predominance of plagioclase feldspar (90–100%), and a minimal mafic component (0–10%). Pyroxene, ilmenite, magnetite, and olivine are the mafic minerals most commonly present.

What is zoning in mineralogy?

Zoning results from the mineral’s inability to maintain chemical equilibrium with a magma during rapid cooling; the zonation represents a frozen picture of the continuous reaction series for that mineral. Zoning can be of three types, the first two applying mostly to plagioclase feldspars.

What is Oligoclase used for?

THE MINERAL OLIGOCLASE. Chemistry: Na(90-70%) Ca(10-30%) (Al, Si)AlSi2 O8, Sodium calcium aluminum silicate. Uses: ornamental and semi-precious stone and as mineral specimens.

What color is Oligoclase?

Oligoclase is a high sodium feldspar crystallizing in the triclinic system. The Mohs hardness is 6 to 6.5 and the specific gravity is 2.64 to 2.66. The refractive indices are: nα=1.533–1.543, nβ=1.537–1.548, and nγ=1.542–1.552. In color it is usually white, with shades of grey, green, or red.

What are the four groups of silicate minerals?

The most common silicate minerals fall into four types of structures, described in more detail below: isolated tetrahedra, chains of silica tetrahedra, sheets of tetrahedra, and a framework of interconnected tetrahedra.

What is the composition of anorthosite?

anorthosite, type of intrusive igneous rock composed predominantly of calcium-rich plagioclase feldspar. All anorthosites found on Earth consist of coarse crystals, but some samples of the rock taken from the Moon are finely crystalline. Most anorthosites formed during Precambrian times.

What is the composition of Lamprophyre?

Lamprophyre Composition Lamprophres is all term for ultrapotassic mafic igneous rocks which have primary mineralogy consisting of amphibole or biotite, and with feldspar in the groundmass. Four minerals dominate these rocks: orthoclase, plagioclase, biotite, and hornblende.

What is compositional zoning?

Compositional zoning is a common feature of pyroclastic deposits erupted from calderas worldwide (Smith 1979; Hildreth 1981; Bacon & Druitt 1988; De Silva 1991; Feeley & Davidson 1994).

Why zoning is common in plagioclase?

Growth of plagioclase crystals accompanied by rapid cooling and contemporaneous crystallisation with falling temperature is considered to cause disequilibrium due to incomplete reaction between the growing crystal and the residual sodic melt. This causes the formation of normal zoning.

Is anorthosite an intermediate?

Proterozoic anorthosites are typically >90% plagioclase, and the plagioclase composition is commonly between An40 and An60 (40–60% anorthite). This compositional range is intermediate, and is one of the characteristics which distinguish Proterozoic anorthosites from Archean anorthosites (which are typically >An80).

What is Allotriomorphic texture?

Allotriomorphic refers to a texture in which all the component mineral grains are anhedral.

What is Ophitic texture in geology?

Ophitic texture is the association of lath-shaped euhedral crystals of plagioclase, grouped radially or in an irregular mesh, with surrounding or interstitial large anhedral crystals of pyroxene; it is characteristic of the common rock type known as diabase.

What is oscillatory zoning in plagioclase?

Oscillatory zoning can be explained as a crystal’s response to fluctuating external conditions. Bowen (1928), for example, attributed it to recycling of plagioclase phenocrysts through zones of cooler, more evolved melt and hotter, more primitive melt in a convecting magma chamber.

Why is plagioclase zoned?