Cordierite
Mg, Fe, Al cyclosilicate mineral / From Wikipedia, the free encyclopedia
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Not to be confused with Cordierites.
"Praseolite" redirects here. For the green variety of quartz, see prasiolite.
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: (Mg,Fe)2Al3(Si5AlO18) to (Fe,Mg)2Al3(Si5AlO18).[3] A high-temperature polymorph exists, indialite, which is isostructural with beryl and has a random distribution of Al in the (Si,Al)6O18 rings.[4] Cordierite is also synthesized and used in high temperature applications such as catalytic converters and pizza stones.
Quick Facts General, Category ...
Cordierite | |
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General | |
Category | Cyclosilicate |
Formula (repeating unit) | (Mg,Fe)2Al4Si5O18 |
IMA symbol | Crd[1] |
Strunz classification | 9.CJ.10 |
Dana classification | 61.02.01.01 Cordierite group |
Crystal system | Orthorhombic |
Crystal class | Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) |
Space group | Cccm |
Unit cell | a = 17.079 Å, b = 9.730 Å, c = 9.356 Å; Z = 4 |
Identification | |
Color | Blue, smoky blue, bluish violet; greenish, yellowish brown, gray; colorless to very pale blue in thin section in transmitted light |
Crystal 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 scale hardness | 7–7.5 |
Luster | Greasy or vitreous |
Streak | White |
Diaphaneity | Transparent to translucent |
Specific gravity | 2.57–2.66 |
Optical properties | Usually optically (-), sometimes (+); 2V = 0–90° |
Refractive index | nα = 1.527 – 1.560 nβ = 1.532 – 1.574 nγ = 1.538 – 1.578 Indices increase with Fe content. |
Pleochroism | X = pale yellow, green; Y = violet, blue-violet; Z = pale blue |
Fusibility | on thin edges |
Diagnostic features | Resembles quartz, can be distinguished by pleochroism. Can be distinguished from corundum by its lower hardness |
References | [2][3][4][5] |
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