Andradite
| Andradite Garnet | |
|---|---|
| Chemical composition | Ca3Fe2(SiO4)3
Calcium Iron Silicate |
| Crystal system | Cubic |
| Habit | Dodecahedra |
| Cleavage | None |
| Hardness | 6.5 |
| Optic nature | Isotropic |
| Refractive index | 1.85-1.89 |
| Birefringence | None |
| Specific gravity | 3.85 |
| Lustre | Vitreous to adamantine |
Contents
Diagnostics
Color
Green, yellow-green and black.
Inclusions
- Fine curving asbestos fibres in a radiating pattern ("horse-tail") in demantoid.
Refractometer
With an RI of about 1.89, the readings are outside the limit of the standard gemological refractometer.
Specific gravity
Sinks in all common heavy liquids.
Chelsea Color Filter
Demantoid appears reddish or pinkish.
Spectroscope
Demantoid has a specific pattern due to iron and chromium.
Dispersion
The dispersion in andradite garnets is high (0.057) and is partially masked by body color.
Varieties
Demantoid
Demantoid is the green variety of andradite.
Melanite
Melanite is the black, opaque variety which is mostly used in mourning jewelry.
Topazolite
Topazolite is the lemon yellow variety of andradite.
Grandite
Photo courtesy of
Wild Fish Gems
Grandite is a brownish variety of grossular-andradite and has lower values compared to the other varieties of andradite. It's name is often used to indicate the whole grossular-andradite intermediate series. Refractive index: 1.780-1.82
