sunbādağ (Corundum/Emery)

Evidence

"(1) Var. ruby in gneiss. 115 x 85 mm, 0.79 kg. (Inventory No. K 3.27a) (2) Var. emery. 85 x 85 mm, 0.206 kg. (Inventory No. K 3.27b)"

Remarks

Sunbādağ is a Persian term. It is a hard stone used to grind metal and stone. It is considered a 'deputy' (nā’ib) of diamond due to its hardness (p. 167). Al-Biruni refers to it as yāqūt aḥmar (p. 167). Corundum is still used in the production of emery paper (p. 167).