Corundum – “Sapphire”
Refractive Index low
ne 1,757 - 1,770
Refractive Index high
no 1,765 - 1,779
Birefringence
0.008 - 0.009
Density
3.97 - 4.10
Polariscope
1 negative
Colours:
colourless, grey, yellow, blue, pink, red, violet, orange, green, purple
Transparency:
Transparent, Translucent, Opaque
Pleochroism:
blue: violet blue/greenish-blue; yellow : yellow/light yellow; green: yellow-green/greenish-yellow; violet: violet/light red to colourless; orange: yellow-brown or orange/colourless; brownish orange: brownish orange/greenish; padparadsha: orange-yellow
UVL:
yellow/orange with colour centre: pinkish orange
UVS:
yellow/orange with colour centre: weak yellow-orange
Remarks:
inclusions: rutile (silk), zircon, apatite, calcite, spinel, uanopyrochlor, etc., healing cracks, liquid and two-phase inclusions, negative crystals, hollow tubes, (boehmite tubes), twinning lamellas, angular growth zoning, colour zoning
absorbtion spectrum: (blue, green, yellow): bands in the blue at 470,460 and 450nm; =>SPECTRUM
Red color: see Ruby
Hardness:
9 - 9
Formula:
AI2O3
System:
Trigonal
Rare?
1