Is a aluminium oxide hydroxide α-AlO(OH); occur in whitish grey colors, sometimes light violet and often change colors if exposed under fluorescent and incandescent light ( see photos)
The best gem material comes from Turkey like this gem here, not common and quite difficult to cut and polish, due to his perfect cleavage. The hardness is 6.5-7.
This gem is eye clean and shows a moderate color change.
Weight: 2.87 ct.