microcline

{{Infobox mineral | name = Microcline | boxwidth = | boxbgcolor = | image = Microcline-199473.jpg | imagesize = | alt = | caption = | struct image = | struct caption = | struct imagesize = | struct2 image = | struct2 caption = | struct2 imagesize= | SMILES = | Jmol = | category = Tectosilicate minerals | group = Feldspar group | series = Alkali feldspar series | formula = KAlSi3O8 | IMAsymbol = Mcc | IMAstatus = Grandfathered (1830) | molweight = | strunz = 9.FA.30 | dana = 76.1.1.5 | system = Triclinic | class = Pinacoidal () | symmetry = P (no. 2) | unit cell = | color = White, grey, greyish yellow, yellowish, tan, salmon-pink, bluish green, green. | habit = Can be anhedral or euhedral. Grains are commonly elongate with a tabular appearance. May contain lamellae which formed from exsolved albite. | 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". thumb|200px|Photomicrograph of [[thin section of microcline showing crosshatched crystal twinning (in cross polarized light)]] | cleavage = 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. | fracture = Uneven | tenacity = Brittle | toughness = | mohs = 6–6.5 | luster = Vitreous | streak = White | diaphaneity = Transparent, translucent | gravity = 2.5–2.6 | density = | polish = | opticalprop = Biaxial negative | refractive = nα = 1.514 – 1.529 nβ = 1.518 – 1.533 nγ = 1.521 – 1.539 | birefringence = Up to first order white (roughly 0.007) | pleochroism = N/A | 2V = 65–88° | dispersion = | extinction = Inclined extinction to cleavage | length fast/slow = | fluorescence = | absorption = | melt = | Curie temp = | fusibility = | diagnostic = Gridiron twinning distinguishes microcline from other feldspars. Distinguishable from plagioclase because the lamellae in plagioclase are continuous and do not "pinch and swell." | solubility = | impurities = | alteration = Commonly alters to sericite or clay. | other = | prop1 = Relief | prop1text = Low negative relief | var1 = | var1text = | var2 = Optical sign | var2text = Biaxial negative | var3 = Color in PPL | var3text = Colorless | var4 = | var4text = | var5 = | var5text = | var6 = | var6text = | references = }} Microcline (KAlSi3O8) is an important igneous rock-forming tectosilicate mineral. It is a potassium-rich alkali feldspar. It is common in granite and pegmatites. Microcline forms during slow cooling of orthoclase. Sanidine is a polymorph of alkali feldspar stable at yet higher temperature. Microcline has cross-hatch twinning that forms as a result of the transformation of monoclinic orthoclase into triclinic microcline.

The chemical compound name is potassium aluminium silicate, and it is known as E number reference E555.