metamorphic
Kyanite in Quartz
Kyanite (Al2SiO5) with Quartz (SiO2)
Hardness: 4.5-5 (along long axis), 6.5-7 (across short axis); Color: Blue, bluish-gray, or grayish-green; Luster: Vitreous to pearly; Crystal structure: Triclinic elongated bladed crystals; Cleavage: Perfect in one direction.
- Hardness
- 4
- Color
- Blue, bluish-gray, or grayish-green
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 4.5-5 (along long axis), 6.5-7 (across short axis); Color: Blue, bluish-gray, or grayish-green; Luster: Vitreous to pearly; Crystal structure: Triclinic elongated bladed crystals; Cleavage: Perfect in one direction.
Formation & geological history
Formed during high-pressure regional metamorphism of clay-rich sedimentary rocks, typically found in schists and gneisses associated with mountain-building events.
Uses & applications
Industrial use in refractory products like spark plugs and porcelain; also used as a gemstone (cabochons) and highly sought after by mineral collectors.
Geological facts
Kyanite is a polymorph with andalusite and sillimanite; they shared the same chemistry but different structures. It is one of the few minerals that has a significantly different hardness depending on the direction it is scratched.
Field identification & locations
Identify in the field by the distinct bladed crystal habit and its varying hardness. Common locations include Brazil, Switzerland, Russia, and the Appalachian Mountains in the USA (specifically North Carolina).
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