Ontario Mineral - Corundum

 

Rocks minerals Ontario Corundum
Chemistry:
 Al2O3, Aluminum Oxide
Class:
 Oxides and Hydroxides
Subclass:
  
Group:
 Hematite
Uses:
 As a gemstone, mineral specimens and as an abrasive.
Color:
 highly variable. The color can be white or colorless, blue, red, yellow, green, brown, purple, and pink; there are also instance of color zonation.
Luster:
 vitreous to adamantine
Transparency:
 Crystals are transparent to translucent
Crystal System:
 trigonal; bar 3 2/m
Crystal Habits:
 include sapphire's typical six-sided barrel shape that may taper into a pyramid, and ruby's hexagonal prisms and blades.
Cleavage:
absent, although there is parting which occurs in three directions.
Fracture:
 conchoidal
Hardness:
 9
Specific Gravity:
 approximately 4.0+ (above average for translucent minerals)
Streak
 white
Other Characteristics:
 Refractive index is around 1.77; pleochroic (meaning color intensity is variable from different viewing directions); striations on parting surfaces.
Associated Minerals:
 calcite, zoisite, feldspars, micas and garnets
Local Occurance:
 Burgess Mine, Egan Chute, Gutz Farm, Lily Robertson
Best Field Indicators:
 extreme hardness, density and crystal habit.

Description:

When someone lists the most famous gemstones such as diamond, topaz, aquamarine, emerald and garnet, corundum does not usually get mentioned. However, its two varieties are sure to be on any list of gemstones. The red variety of corundum is known as ruby and all the other colors of corundum are known as sapphire.
Corundum is the second hardest natural mineral known to science. The hardest mineral, diamond is still four times harder than corundum. The hardness of corundum can be partially attributed to the strong and short oxygen-aluminum bonds. These bonds pull the oxygen and aluminum atoms close together, making the crystal not only hard but also quite dense for a mineral made up of two relatively light elements.