Chemical formula: Al2O3

Composition: Aluminum oxide

Mineral of the Month: November 2014

Color: Many colors, including blue, red, violet, pink, green, yellow, orange, gray, white, colorless, and black. Occasionally also it is multicolored and/or striped.

Streak: White

Hardness: 9

Crystal System: Hexagonal

Rock type: Igneous, metamorphic

Environments: In altered metamorphic rocks such as marble and hornfels, in nepheline syenite pegmatites, and in placer deposits.


  • Emery- black, massive variety where the color is a mixture of Magnetite, Hematite, and Spinel.
  • Padparadschah- Orange-pink gem variety of Sapphire. Padparadschah is a very rare and sought after variety
  • Ruby- Pink to red variety of Corundum. (Contains traces of Cr.)
  • Sapphire- Refers to all gem varieties of Corundum, excluding the red variety of Corundum, ruby. Sapphire usually refers to the blue, blue-green, or green sapphires. When a color other than blue though, it is commonly referred to as “fancy” in the gem trade.(Contains traces of Fe and Ti.)
  • Star Ruby and Star Sapphire are where the stone displays an asterism in the form of a six- and sometimes twelve- ray star.
  • Ultralite is an incorrect term used in the gem trade to describe the blue Sapphire.


Aside from being the second and third most popular gemstones in the world, diamond taking first, it is also used as an industrial abrasive. Emery cloth is a blend of the aluminum oxide, Al2O3 with a blend of Magnetite, Hematite, and Spinel.

Corundum is easily created in the lab. Many rubies and sapphires found in the marketplace are artificial.

The first laser was made with an artificial ruby in 1960.

Corundum is also used in watches where the bearings need to be strong and long lasting with minimal friction.

Corundum is used in making abrasive wheels, power driven and hand driven. One of the common forms is the emery boards used to shape finger nails.



Ruby in matrix


Ruby Crystal



Ruby and Sapphire Crystals, gravel wash from mine.


Sapphire crystal cluster


lightly tumbled mine run, sapphire and ruby

black corundum from Ontario burgess mine

Black corundum


Sapphire crystal

ruby - trapiche from Burma

Trapiche Ruby, aka Star Ruby, star shape caused by the impurity lutite.

ruby in Zoisite

Ruby in Zoisite

sapphire brazil 

Sapphire crystals

star ruby Burma

Trapiche Ruby

Macon, Georgia 31210