GPFDC
From The Gemology Project
<math>{n \choose k}</math> <math>\int_{-N}^{N} e^x\, dx</math>
Diamond | |
---|---|
Chemical composition | C |
Crystal system | Cubic |
Habit | Octahedral, cubic |
Cleavage | Perfect (octahedral) |
Fracture | Conchoidal |
Hardness | 10 |
Optic nature | Isotropic |
Refractive index | 2.417 |
Birefringence | None |
Dispersion | High, 0.044 |
Specific gravity | 3.52 |
Lustre | Adamantine |
Pleochroism | None |
Corundum | |
---|---|
Chemical composition | Al2O3 |
Crystal system | Trigonal |
Habit | Prismatic, tabular |
Cleavage | None; twinned stones may show parting |
Fracture | Conchoidal |
Hardness | 9 |
Optic nature | Uniaxial - |
Refractive index | 1.762-1.770 (+.009,-.005) |
Birefringence | 0.008-0.010 |
Dispersion | Low, 0.018 |
Specific gravity | 4 |
Lustre | Vitreous to Subadamantine |
Pleochroism | Weak to moderate |
Kyanite | |
---|---|
Chemical composition | Al[sub]2[/sub]SiO[sub]5[/sub] |
Crystal system | triclinic |
Habit | bladed |
Cleavage | parallel to prism face |
Fracture | splintery or fibrous |
Hardness | 7 across the crystal, 5 along the length |
Optic nature | trichroic |
Refaction index | 1.715-1.732 |
Birefringence | 0.017 |
Dispersion | low, 0.011 |
Specific gravity | 3.58 |
Lustre | vitreous |
Pleochroism | pronounced violet-blue, colorless, and blue |