Topaz is a kind of aluminosilicate chloride or hydroxide. It belongs to the orthorhombic mineral. The refractive index is 1.619-1.637, the birefringence difference is 0.008-0.010, the specific gravity is about 3.53, and the hardness is 8. , Second only to red sapphire corundum, but its toughness is very poor, because the topaz crystal has a […]
