Properties
| Category | Cyclosilicate |
|---|---|
| Formula | (Mg,Fe)2Al4Si5O18 |
| Crystal system | Orthorhombic |
| 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 |
| 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 |
From the Wikipedia article
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). A high-temperature polymorph exists, indialite, which is isostructural with beryl and has a random distribution of Al in the (Si,Al)6O18 rings. Cordierite is also synthesized and used in high temperature applications such as catalytic converters and pizza stones.
Source
Source record: crystal-compendium/iolite/minerals.json. Fetched from English Wikipedia by the operator 2 October 2026.
https://en.wikipedia.org/wiki/Cordierite — revision id 1328193348. Text and properties from Wikipedia, licensed CC BY-SA 4.0.