What is Perthitic texture?

Asked By: Elisha Dudchik | Last Updated: 12th February, 2020
Category: science geology
4.3/5 (212 Views . 12 Votes)
A perthite is an intimate intergrowth of sodic and potassic feldspar resulting from subsolidus exsolution (unmixing of two minerals). An Antiperthite is an intergrowth arising due to exsolution where potassic feldspar is present as blebs or lamellae within a sodic feldspar.

Click to see full answer

Likewise, people ask, what is Exsolution?

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.

One may also ask, which feldspar is pink? Orthoclase

Also know, which feldspar has exsolution lamellae?

Perthite is used to describe an intergrowth of two feldspars: a host grain of potassium-rich alkali feldspar (near K-feldspar, KAlSi3O8, in composition) includes exsolved lamellae or irregular intergrowths of sodic alkali feldspar (near albite, NaAlSi3O8, in composition).

What are alkali feldspars?

Alkali feldspar, any of several common silicate minerals that often occur as variously coloured, glassy crystals. In the Earth's crust the alkali feldspars display a range of ordering from the fully random distribution of sanidine and orthoclase to the fully ordered distribution of microcline. See feldspar.

34 Related Question Answers Found

How is pyroxene formed?

The two mineral groups are related to one another, as during metamorphism water reacts with pyroxene minerals to convert them to amphibole. So pyroxenes are more common in rocks that formed in water-free settings, while amphiboles are more common in water-wet rocks or during late water-rich stages of magma cooling.

How do you identify Quartz in a thin section?

In thin section, when viewed in plane polarized light (PPL), quartz is colorless with low relief and no cleavage. Its habit is either fairly equant or anhedral if it infills around other minerals as a cement.

Is Augite a pyroxene?

Augite is a common rock-forming pyroxene mineral with formula (Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6. The crystals are monoclinic and prismatic. Augite has two prominent cleavages, meeting at angles near 90 degrees.

What is a mineral Pseudomorph?

In mineralogy, a pseudomorph is a mineral or mineral compound that appears in an atypical form (crystal system), resulting from a substitution process in which the appearance and dimensions remain constant, but the original mineral is replaced by another. The name literally means "false form".

What is solid solution in geology?

Solid solution, mixture of two crystalline solids that coexist as a new crystalline solid, or crystal lattice. The substances may be soluble over a partial or even complete range of relative concentrations, producing a crystal whose properties vary continuously over the range.

What mineral group is plagioclase feldspar in?

Plagioclase is a member of the feldspar group (like orthoclase) and is a framework silicate. Plagioclase consists of a solid solution between the albite and anorthite end-members, and together with quartz is the most common of the rock forming minerals.

Which texture is typical of granite?

Granites are intrusive felsic rocks (from the Latin “granum” means “grain”) usually hypidiomorphic (greater proportion of subhedral crystal forms) and typically granular texture (Fig. 4.6(A)). The grain size varies between fine (Figs 4.10 and 4.11), medium and coarse.

Which mineral has the highest specific gravity?

Osmium probably has the highest Specific Gravity among minerals approved by the IMA.

What is potassium feldspar?

Potassium feldspar refers to a number of minerals in the feldspar group, and containing potassium: Orthoclase (endmember formula KAlSi3O8), an important tectosilicate mineral that forms igneous rock. Microcline, chemically the same as orthoclase, but with a different crystalline structure.

What is polysynthetic twinning?

Noun. polysynthetic twinning (usually uncountable, plural polysynthetic twinnings) (geology) A type of contact twinning, typically observed in plagioclase, in which the composition surfaces are parallel to one another.

Does feldspar have cleavage?

Feldspars have two cleavage planes that intersect at 90°. Fragments of pure feldspar crystals thus tend to form rectangular blocks with irregular ends. Feldspars have vitreous lusters and occur in opaque shades of white to gray to pink to very dark gray.

What is Carlsbad twinning?

Definition of carlsbad twin. A twinned crystal in which the twinning axis is the c axis, the operation is a rotation of 180 degrees, and the contact surface is parallel to the side pinacoid. It is quite common in the alkali feldspars. An alternative spelling is Karlsbad twin.

What color is quartz?

Pure quartz is white or colorless, but is commonly found in almost any color imaginable. Since quartz is naturally clear, any chemical impurities will allow the color to "shine" through. Amethyst, tiger eye, adventurine, and agates are all varieties of quartz with impurities in them to cause their distinctive color.

What does feldspar look like?

Feldspars usually are white or nearly white, though they may be clear or light shades of orange or buff. They usually have a glassy luster. Feldspar is called a rock-forming mineral, very common, and usually makes up a large part of the rock. Other differences: quartz is usually clear and feldspar is usually cloudy.

What is the Colour of feldspar?

In general, potassium feldspars commonly have pink to reddish hues, while the plagioclase feldspars tend to be white or gray, but both mineral groups may exhibit similar colors, so the presence or absence of striations is more diagnostic.

How do you identify pyroxene?

Pyroxene Minerals
  1. Shape: Orthorhombic or monoclinic.
  2. Luster: Glassy or metallic.
  3. Color: Black.
  4. Streak: White, light green or light brown.
  5. Hardness: 5-6.5 on Mohs Hardness Scale.
  6. Cleavage: Two planes that meet at nearly a 90-degree angle.
  7. Fracture: Most have uneven and brittle fractures.

What is quartz made of?

' Quartz is an igneous rock that is composed of oxygen and silicon atoms in a continuous makeup of silicon-oxygen tetrahedra (SiO4). Each individual oxygen atom is shared between two tetrahedra atoms, giving quartz the final chemical formula scientifically known as SiO2.