Tagged “hardness”

Entries across every discipline that share this thread.

Gemstone

Pure crystalline carbon — the hardest natural material and the enduring symbol of the precious stones.

Gemstone

The red variety of corundum — second only to diamond in hardness, and coloured by chromium.

Gemstone

Corundum in every colour but red — famed for its blue, and prized for durability.

Gemstone

A hard aluminium fluorosilicate spanning colourless to imperial orange — with a notable cleavage to respect.