What is Perthitic texture?

Strictly speaking a perthite has blebs or irregular lamellae of sodic feldspar within potassic alkali feldspar, however, the term perthite is often used to describe all types of exsolution in the feldspars.

How do you identify perthite?

In perthite, they sometimes may be seen by the unaided eye; in microperthite, however, they are distinguishable only microscopically, and in cryptoperthite the crystals are so small that the separation can be detected only by X-ray diffraction.

What is perthite and antiperthite?

Antiperthite is albitic plagioclase with small discrete K-feldspar that has become exsolved from the albite. To distinguish the difference between perthite and antiperthite is to determine which the predominant feldspar is. If K-feldspar predominates, it is a perthite. If Albite predominates, it is an antiperthite.

What is the texture of orthoclase?

Orthoclase Mineral Data

Is perthite a mineral?

Usually perthite consists of brown and white lamellae; the white feldspar often has a golden yellow or white Schiller. Perthitic intergrowths are very typical of the whole range of plagioclase compositions and therefore must be considered one of the most abundant mineral associations in nature.

Is perthite a plagioclase?

Perthite is the name given to an intergrowth of K-feldspar and albite-rich plagioclase that is produced by exsolution of the plagioclase from the potassium feldspar upon cooling of an original higher temperature, homogeneous solid solution of the two minerals.

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 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.

What is exsolution solid solution?

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. In most cases, it occurs upon cooling below the temperature of mutual solubility or stability of the solution.

Is clinopyroxene a Pleochroic?

Clinopyroxene – XYZ₂O. Optical properties: Colour and Pleochroism: Usually colourless, gray, pale green or pale brown, darker colours associated with Fe-rich varieties titanaugite is more distinctly coloured from brown/pink to violet. Cleavage: Parallel to {110}, which intersect at 90°.

Is diopside a clinopyroxene?

Diopside, a Ca-Mg clinopyroxene is found mostly in marbles. Clinopyroxenes have general formula (Ca,Mg,Fe,Na)(Mg,Fe,Al)(Si,Al)₂O₆.

Is Quartz a pleochroic?

Pleochroism: None. Cleavage/fracture: No cleavage, but fractures and healed fractures can be common. Relief and optic sign: Low; uniaxial (+).

How can you tell the difference between clinopyroxene and orthopyroxene?

In orthopyroxenes the M2 site is usually octahedral and commonly contains Fe and Mg. In clinopyroxenes, larger cations (such as Li and Na) are in eightfold coordination in the M2 site (the larger cations need a different geometry to accommodate them, which reduces the symmetry to monoclinic).

How do I know if I have orthopyroxene?

The keys to identifying orthopyroxene are its relief, usually pale green (sometimes pleochroic to pink) color, low-order interference colors, and near 90^o cleavage seen in some views. Color – Commonly light green, but some orthopyroxene shows marked pleochroism to pink. Relief is moderate to fairly high.

What is orthopyroxene mineral?

orthopyroxene, any of a series of common silicate minerals in the pyroxene family. Orthopyroxenes typically occur as fibrous or lamellar (thin-plated) green masses in igneous and metamorphic rocks and in meteorites.

Does orthopyroxene have cleavage?

A diagnostic feature of members of the pyroxene group is the {110} cleavage that intersects at approximately 90 degrees, as seen in one of the orthopyroxene grains near the centre of these images.

Is Augite a Pleochroic?

Color: Colorless, pale green, pale brown, green, greenish-yellow, pale yellow green, grayish green, violet. Zonal structure is sometimes present. Pleochroism: Absent or weak; it is best shown in {100} sections.

Is actinolite a Pleochroic?

Strong brown or green coloration and pleochroism, and 60^o-120^o cleavage angles identify hornblende. Actinolite is similar, but its color ranges from light green (Fe-poor varieties) to dark green (Fe-rich varieties).

Is Pleochroic a biotite?

In thin section, biotite exhibits moderate relief and a pale to deep greenish brown or brown color, with moderate to strong pleochroism. Biotite has a high birefringence which can be partially masked by its deep intrinsic color.

What texture is biotite?

This rock is mostly composed of creamy-white feldspar and quartz, together with dark minerals, of which the most abundant is the dark mica biotite. The dark minerals are arranged in a streaky banding, giving the rock a gneissic texture.

What color is amphibole?

Identification: Typically, amphiboles form as long prismatic crystals, radiating sprays and fibrous aggregates. They are generally dark coloured though their colours can range from colourless to white, green, brown, black, blue or lavender. This property is related to composition, particularly iron content.

What type of rock is biotite?

igneous rocks

biotite, also called black mica, a silicate mineral in the common mica group. It is abundant in metamorphic rocks (both regional and contact), in pegmatites, and also in granites and other intrusive igneous rocks. For chemical formula and detailed physical properties, see mica (table).

Is biotite igneous sedimentary or metamorphic?

Biotite is a rock-forming mineral found in a wide range of crystalline igneous rocks such as granite, diorite, gabbro, peridotite, and pegmatite. It also forms under metamorphic conditions when argillaceous rocks are exposed to heat and pressure to form schist and gneiss.

What is a biotite schist?

For example, a quartz-feldspar-biotite schist is a schist of uncertain protolith that contains biotite mica, feldspar, and quartz in order of apparent decreasing abundance. Lineated schist has a strong linear fabric in a rock which otherwise has well-developed schistosity.