cordierite

{{Infobox mineral |boxbgcolor=#7e7066| name = Cordierite | boxtextcolor = #fff | category = Cyclosilicate | image = Cordierite-den07-06aa.jpg | imagesize = 260px | caption = | formula = | IMAsymbol = Crd | strunz = 9.CJ.10 | dana = 61.02.01.01 Cordierite group | system = Orthorhombic | class = Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) | symmetry = Cccm | unit cell = a = 17.079 Å, b = 9.730 Å, c = 9.356 Å; Z = 4 | color = Blue, smoky blue, bluish violet; greenish, yellowish brown, gray; colorless to very pale blue in thin section in transmitted light | habit = Pseudo-hexagonal prismatic twins, as imbedded grains, and massive | twinning = Common on {110}, {130}, simple, lamellar, cyclical | cleavage = Fair on {100}, poor on {001} and {010} | fracture = Subconchoidal | tenacity = Brittle | mohs = 7–7.5 | luster = Greasy or vitreous | diaphaneity = Transparent to translucent | refractive = nα = 1.527 – 1.560 nβ = 1.532 – 1.574 nγ = 1.538 – 1.578 Indices increase with Fe content. | opticalprop = Usually optically (-), sometimes (+); 2V = 0–90° | pleochroism = X = pale yellow, green; Y = violet, blue-violet; Z = pale blue | streak = White | gravity = 2.57–2.66 | melt = | fusibility = on thin edges | diagnostic = Resembles quartz, can be distinguished by pleochroism. Can be distinguished from corundum by its lower hardness | solubility = | other = | references = }}

Cordierite (mineralogy) or iolite (gemology) is a magnesium iron aluminium cyclosilicate. Iron is almost always present, and a solid solution exists between Mg-rich cordierite and Fe-rich sekaninaite with a series formula: to . A high-temperature polymorph exists, indialite, which is isostructural with beryl and has a random distribution of Al in the rings. Cordierite is also synthesized and used in high temperature applications such as catalytic converters and pizza stones.