Information For precious and semi precious gemstones
Stone : Black Spinel
Moh's Hardness : 8
Origin Locations : Rubyvale, Central Queensland sapphire fields, Australia; Burma; Minas Gerais, Brazil; Tanzania; Nigeria; Thailand
Treatments : None
Clarity : Opaque
Color : Black
Cleavage : Indistinct
Crystal System : (Cubic), octahedron, twins, rhombic dodecahedron
Chemical Composition : (Mg,Fe) Al2O4
Refractive Index (RI) : N/A
Density : 3.63-3.90
Comments : Black spinels are a true member of the spinel family but whereas the coloured spinels like red, blues, etc are transparent, black spinel is opaque. This is the same as black tourmaline. Black spinel is also known as Pleonaste and Ceylonite. The black spinel that comes from the Central Queensland sapphire fields is a very pure black and takes a glossy shiny polish, though it is very messy to cut!
Most black stones in the marketplace, such as black onyx and black diamonds (yes, you can get natural black diamonds but the vast majority of commerical black diamonds...) have been treated either by irradiation, heating or have been dyed. Black spinels are completely natural and have not been treated in any way. Jet is another black stone and has often been used in mourning jewelry however it is quite soft at 2.5 - 4 on the Moh's hardness scale.
If you are looking for a good black gemstone that hasn't been treated and is suitable for jewelry then black spinel is for you.