Color is dark azure-blue to a bright indigo blue or even a pale sky blue. Luster is vitreous to dull. Specimens are translucent to less commonly transparent. Also granular and massive. Cleavage is distinct in one direction.
Fracture is uneven.
Hardness is 5.5 - 6. Streak is pale blue to white. Associated Minerals are quartz , rutile , kyanite , andalusite , garnets , muscovite , corundum , wardite , brazilianite and siderite .