Which feldspar has exsolution lamellae?

K-feldsparpotassium-rich alkali feldspar (near K-feldspar, KAlSi₃O₈, in composition) includes exsolved lamellae or irregular intergrowths of sodic alkali feldspar (near albite, NaAlSi₃O₈, in composition).

Does plagioclase feldspar have exsolution lamellae?

Plagioclase feldspars

The play of colors visible in some feldspar of labradorite composition is due to very fine-grained exsolution lamellae known as Bøggild intergrowth. The specific gravity in the plagioclase series increases from albite (2.62) to anorthite (2.72–2.75).

Does potassium feldspar have lamellae?

Potassium feldspar (also orthoclase feldspar or K-spar) exhibits bands of different color on cleavage surfaces. These bands, or exsolution lamellae, are planar zones of slightly different composition.

Does plagioclase have exsolution?

Plagioclase feldspars exhibit exsolution microtextures in three compositional ranges, the Peristerite, Bøggild and Huttenlocher ‘miscibility gaps’ shown in orange on Fig. 4 and in white in Fig. 8. These intergrowths are coherent and usually below the resolution of an optical microscope.

What are exsolution lamellae?

Exsolution lamellae are fine crystals that were dissolved entirely in their host mineral structures at high temperature (e.g., clino- and orthopyroxenes) and/or pressure (e.g., majorite-pyroxenes), but are produced when their host minerals lose the solubility as a result of cooling to low temperatures (T-controlled …

What is exsolution lamellae in geology?

Exsolution is a process by which a solid solution phase unmixes into two separate phases in the solid state. Exsolution occurs only in minerals whose compositions vary between two or more pure endmember compositions.

What is exsolution in geology?

exsolution, in mineralogy, process through which an initially homogeneous solid solution separates into at least two different crystalline minerals without the addition or removal of any materials.

What is Orthopyroxene made of?

In Earth’s crust, pyroxenes are found in a wide range of igneous and metamorphic rocks. They are most abundant in the dark-colored igneous rocks, such as basalt and gabbro, that comprise most of the oceanic crust.

Is Pigeonite a Clinopyroxene?

Pigeonite is a mineral in the clinopyroxene subgroup of the pyroxene group. It has a general formula of (Ca,Mg,Fe)(Mg,Fe)Si ₂O ₆.

What is Poikilitic texture in geology?

Poikilitic texture describes the occurrence of one mineral that is irregularly scattered as diversely oriented crystals within much larger host crystals of another mineral.

Is quartz an aphanitic?

Aphanites are commonly porphyritic, having large crystals embedded in the fine groundmass, or matrix. The larger inclusions are called phenocrysts. They consist essentially of very small crystals of minerals such as plagioclase feldspar, with hornblende or augite, and may contain also biotite, quartz, and orthoclase.

Which rock shows Ophitic texture?

This texture is found in granites. Ophitic texture – laths of plagioclase in a coarse grained matrix of pyroxene crystals, wherein the plagioclase is totally surrounded by pyroxene grains. This texture is common in diabases and gabbros.

What is fragmental texture?

A texture of sedimentary rocks, characterized by broken, abraded, or irregular particles in surface contact, and resulting from the physical transport and deposition of such particles; the texture of a clastic rock. The term is used in distinction to a crystalline texture. Ref: AGI. iii.

Is obsidian aphanitic or phaneritic?

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 fragmental rock?

Fragmental (or clastic) sediments are made up of particles of weathered rock, including rock fragments, residual mineral grains (especially quartz, which is both hard and chemically inert) and clay minerals. Examples include: conglomerate, sandstone, mudstone & shale.

What is the difference between phaneritic and aphanitic rocks?

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.

Is basalt mafic or felsic?

Compilations of many rock analyses show that rhyolite and granite are felsic, with an average silica content of about 72 percent; syenite, diorite, and monzonite are intermediate, with an average silica content of 59 percent; gabbro and basalt are mafic, with an average silica content of 48 percent; and peridotite is …

What is a foliated rock with gneissic banding composed of feldspar mica and quartz?

Texture

Is scoria mafic or felsic?

Scoria and Pumice

Scoria is a mafic volcanic glass. It is an extremely vesicular basaltic lava with very small (< 1mm) vesicles. Pumice is a felsic volcanic glass.

Is rhyolite extrusive or intrusive?

extrusive igneous rock

rhyolite, extrusive igneous rock that is the volcanic equivalent of granite. Most rhyolites are porphyritic, indicating that crystallization began prior to extrusion.

Is pumice basaltic or granitic?

Classification of Igneous Rocks

Is basalt extrusive or intrusive?

extrusive igneous

basalt, extrusive igneous (volcanic) rock that is low in silica content, dark in colour, and comparatively rich in iron and magnesium.

Is gneiss foliated or Nonfoliated?

Foliated metamorphic rocks such as gneiss, phyllite, schist and slate have a layered or banded appearance that is produced by exposure to heat and directed pressure. Non-foliated metamorphic rocks such as hornfels, marble, quartzite and novaculite do not have a layered or banded appearance.

Is andesite extrusive or intrusive?

Igneous Rock Types and Textures. Porphyritic texture — andesite: This is an extrusive igneous rock. The magma from which it formed cooled slowly for a while deep below the surface (forming the large crystals), then finished cooling very quickly when it was ejected at the surface, forming the fine-grained groundmass.

Is shale extrusive?

It is a type of sedimentary rock that is formed by extrusion, dehydration, recrystallization, and cementation of weak clay. It is called shale because it is stratified and easily delaminated.

Is gneiss intrusive or extrusive?

Is gneiss intrusive or extrusive? Many gneisses are made of the same minerals as coarse-grained intrusive rocks such as granite or diorite. This barn wall shows three large gneisses (black and white/pink striped rocks) plus several coarse-grained intrusive rocks.

Is marble extrusive or intrusive?

The majority of stones used for home improvement projects have metamorphic origins. Marble is a metamorphic rock, meaning that it was created via intense heat and pressure. It begins as limestone before the process, which is called metamorphism.