Hardness: 5.0 - 7.0
Specific Gravity: 3.60
Characteristics: Usually blue; polymorph of andalusite and sillimanite; hardness ≈ 5.0 parallel to length of crystal and ≈ 7.0 perpendicular; bladed crystals with perfect cleavage in one direction, good in another; vitreous luster; insoluble in most acids.
Found in high pressure aluminum-rich schists; kimberlites; some eclogites.
Kyanite is used for various refractory purposes, which refers to those that are resistant to high temperatures, such as needed in the production of steel, glass, and heat resistant ceramics.
(Primary text: Perkins, D. 2002. Mineralogy. Prentice Hall.)