How can you tell the difference between between topaz and corundum?
Corundum is harder (hardness 9) than topaz (hardness 8), but the best way to differentiate between them is by crystal form. Topaz is orthorhombic, which means it forms rectangular crystals that have chisel-shaped points, while corundum is hexagonal and forms six-sided crystals that usually don’t have points on the ends.
