Article
Article
Kyanite
Article By:
Holdaway, M. J. Department of Geological Sciences, Southern Methodist University, Dallas, Texas.
Last reviewed:November 2019
DOI:https://doi.org/10.1036/1097-8542.366900
A nesosilicate mineral, Al2SiO5, crystallizing in the triclinic system and occurring in metamorphic rocks. Kyanite is essentially a pure phase, but minor amounts of iron (Fe3+), chromium (Cr3+), and titanium (Ti4+) may substitute for aluminum (Al). Kyanite occurs in well-formed bladed crystals and aggregates. Luster is vitreous to pearly. It is usually light blue (Fig. 1) because of minor Fe and Ti, and, rarely, light green because of Fe only. Kyanite may also be white or gray. Hardness is 5 (Mohs scale) along the length of crystals and 7 at right angles to the length. Kyanite has a single perfect cleavage parallel to the bladed face of crystals. See also: Hardness scales; Metamorphic rocks
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