Cordierite
Image: Didier Descouens (CC BY-SA 3.0)
Mineral NameCordierite
Chemical Formula(Mg,Fe)2Al4Si5O18
Mohs Hardness7
Crystal Systemorthorhombic
Lustervitreous
Streak Colorwhite
CleavageGood on {010}, poor on {100} and {001}
Fractureconchoidal to uneven
Specific Gravity2.65
Colorsblue, violet, purplish-gray
Transparencytransparent
Type LocalityCoimbatore District, Chennai (Madras), Tamil Nadu, India
Mineral GroupSilicates
Usesjewelry, collector
Associated Mineralsquartz, feldspar, garnet, sillimanite, kyanite
Rarityuncommon
Description
This image displays two views of a faceted oval cordierite gemstone, showcasing its strong pleochroism, appearing deep blue in one orientation and a lighter purplish-gray in another. The stone has a vitreous luster and some internal inclusions.
Geological Context
Cordierite typically forms during regional metamorphism of argillaceous rocks, often found in gneisses and schists, or in contact metamorphic aureoles around igneous intrusions. It can also occur in some igneous rocks.
