Optical properties - Microcline
Microcline feldspar
Crystal System:	Triclinic
Color in PPL:	Colorless
Pleochroism:	N/A
Habit/Shape:	Can be anhedral or euhedral. Grains are commonly elongate with a tabular appearance. May contain lamellae which formed from exsolved albite.
Relief:	Low negative relief
Cleavage/Fracture Habit:	Has perfect cleavage parallel to {001} and good cleavage on {010}. Cleavages intersect at 90°41'. It can be difficult to see cleavage in thin section due to microcline's low relief.
Twinning:	Typically displays albite twinning and pericline twinning. This combination leads to a grid pattern, hence microcline displays gridiron twinning. Can also display carlsbad twinning, simple twins, or lack twinning altogether. Lamellae in microcline are discontinuous and "pinch and swell."
Birefringence:	Up to first order white (roughly 0.007)
Extinction Habit/Angle:	Inclined extinction to cleavage
Length Slow/Fast:	N/A
Optic Sign:	Biaxial negative
2Vx:	65-88°
Alteration:	Commonly alters to sericite or clay.
Distinguishing Characteristics:	Gridiron twinning distinguishes microcline from other feldspars. Distinguishable from plagioclase because the lamellae in plagioclase are continuous and do not "pinch and swell."

Microcline (KAlSi₃O₈) is an important igneous rock forming tectosilicate mineral. It is also known as alkali feldspar and is common in granite and related rocks. Commons:Imagem:Feldspar(Microcline)USGOV.jpg File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Commons:Imagem:Feldspar(Microcline)USGOV.jpg File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... In crystallography, the triclinic crystal system is one of the 7 lattice point groups. ... PPL can stand for: An abbreviation for People, often used in IRC and Instant Messengers Private Pilot License Pokémon Puzzle League Phonographic Performance Limited Pennsylvania Power and Light - an electric company Pakistan Petroleum Limited This is a disambiguation page — a navigational aid which lists other pages that might otherwise share... Pleochroism is an optical phenomenon where due to double refraction of light by a colored gem or crystal, the light is divided into two paths which are polarized at a 90° angle to each other. ... In geometry, the dihedral is the angle between two planes. ... Euhedral refers to well formed crystals with sharp easily recognised faces. ... Lamellar structures are gill-shaped structures, with sheets of one material interleaved with another. ... Feldspar (from the German Feld, field, and Spat, a rock that does not contain ore) is the name of an important group of rock-forming minerals which make up perhaps as much as 60% of the Earths crust. ... A calcite crystal laid upon a paper with some letters showing the double refraction Birefringence, or double refraction, is the division of a ray of light into two rays (the ordinary ray and the extraordinary ray) when it passes through certain types of material, such as calcite crystals, depending on... Sericite is a fine grained mica, either muscovite, illite, or paragonite. ... Clay is a generic term for an aggregate of hydrous silicate particles less than 4 μm (micrometres) in diameter. ... Feldspar (from the German Feld, field, and Spat, a rock that does not contain ore) is the name of an important group of rock-forming minerals which make up perhaps as much as 60% of the Earths crust. ... Feldspar (from the German Feld, field, and Spat, a rock that does not contain ore) is the name of an important group of rock-forming minerals which make up perhaps as much as 60% of the Earths crust. ... Igneous rocks are formed when molten rock (magma) cools and solidifies, with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. ... The silicate minerals make up the the largest and most important class of rock-forming minerals. ... This article is about minerals in the geologic sense; for nutrient minerals see dietary mineral; for the band see Mineral (band). ... Granite is a common and widely-occurring group of intrusive felsic igneous rocks that form at great depths and pressures under continents. ...

Microcline is chemically the same as orthoclase, but belongs to the triclinic crystal system, the prism angle being slightly less than right angles; hence the name "microcline" from the Greek "small slope." Microcline is identical to orthoclase in all physical properties and can be distinguished only by optical examination; under a polarizing microscope microcline exhibits a minute multiple twinning which results from a grating-like structure that is unmistakable. It is probable that much orthoclase is actually microcline. In crystallography, the triclinic crystal system is one of the 7 lattice point groups. ... Galvanized surface with macroscopic crystalline features. ...

Feldspar (Amazonite)

Amazon stone, or amazonite, is a beautiful green variety of microcline. It is not found anywhere in the Amazon basin, however, Spanish explorers who named it apparently confused it with another green mineral from that region. Commons:Imagem:Feldspar(Amazonite)USGOV.jpg File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Commons:Imagem:Feldspar(Amazonite)USGOV.jpg File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Feldspar (Amazonite) Amazonite (sometimes called Amazon stone) is a green variety of microcline feldspar. ... emine ==Geography== The South American rainforest of Amazonia (60% located in Brazil), the largest in the world, was originally covered by more than 7,000,000 km² (2 million square miles) of dense tropical forest. ...

A soda microcline named anorthoclase is known, which is an isomorphous mixture of KAlSi₃O₈ and NaAlSi₃O₈, the sodium-aluminium silicate being in larger proportion.

Related topics

• List of minerals

Gem animals. ...

References

• Alkali feldspars U. Texas
• Mindat