Thursday, August 28, 2014


Corundum is a type of gem stone that can be many different colors, red, yellow, pink-orange, green or blue.

If the corundum is red, it is called a ruby. Otherwise it is called a sapphire.

Corundum is very hard and rough, is sometimes used on sandpaper or on large cutting machines.
(from: wikipedia - corundum)

Kid Facts - Blast from the past: Diode