The Mohs' Hardness scale is the 1 - 10 scale of minerals hardness. The blue topaz is number 8 on that list. It's chemical composition is Al2 SiO4 (R,OH)2, which is fluor containing aluminum silicate, which is fluorosilicate (Schumann). Another quality of the blue topaz is that it has perfect cleavage (Schumann). Because of its perfect cleavage, the topaz is susceptible to breaking (King). When scratched, a mineral may leave a streak of a color behind. The blue topaz has a colorless streak (Schumann). The mineral has a vitreous luster (Schumann). Topaz can be cut in a variety of shapes. Topaz can be cut into a square, round, octagon, pear, oval, heart, and many others (About the Blue topaz)
Pear cut Oval cut Heart