mineral
Kyanite blade
Kyanite, Al₂SiO₅
AI-generated identification · may be incorrectPale blue, bladed crystal with pearly to vitreous luster and strong lengthwise striations; Mohs hardness is 4.5 parallel to the blade and 6.5–7 across it, with perfect cleavage in two directions. Commonly forms thin, flattened crystals rather than a granular mass.
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Physical properties
Pale blue, bladed crystal with pearly to vitreous luster and strong lengthwise striations; Mohs hardness is 4.5 parallel to the blade and 6.5–7 across it, with perfect cleavage in two directions. Commonly forms thin, flattened crystals rather than a granular mass.
Formation & geological history
A high-pressure, medium-temperature metamorphic mineral formed mainly in schist and gneiss during regional metamorphism, commonly from Paleozoic to Precambrian rocks. It is an aluminosilicate polymorph of andalusite and sillimanite.
Uses & applications
Used as a refractory material in furnaces, kilns, and ceramics because it expands predictably when heated; attractive blue crystals are also sold as collectible or cabochon jewelry material.
Geological facts
The pronounced hardness anisotropy is diagnostic: a specimen can be scratched easily along its length but not across it. Blue color is typical, though white, gray, orange, and green varieties occur.
Field identification & locations
Identify it by its blue bladed habit, fibrous/striated surface, and directional hardness; distinguish it from sillimanite’s fibrous needles and blue sapphire’s uniform hardness. Common localities include Nepal, Brazil, Switzerland, India, and Virginia, USA.
