Almandine

From The Gemology Project
Revision as of 10:16, 13 December 2006 by Doos (talk | contribs)
Jump to: navigation, search
Almandine Garnet
Chemical composition Fe3Al2(SiO4)3

Iron aluminum silicate

Crystal system Cubic
Habit Dodecahedra
Cleavage None
Hardness 7.5
Optic nature Isotropic
Refractive index 1.78-1.81
Birefringence None
Specific gravity 3.95 - 4.20
Lustre Vitreous

Diagnostics

Color

Brownish red, red to violet/purple

Spectroscope

Almandine has a typical iron spectrum

Inclusions

  • Short rutile needles in 3 directions
  • Crystals surrounded by stress cracks
  • Irregular and rounded crystals

Polariscope

Almandine is isotropic but may have a small DR.

Specific gravity

Sinks in all common heavy liquids

Optical effects

Almandine may show asterism and chatoyancy

Varieties

Rhodolite

Rhodolite is the purple (pinkish/violet) variety of pyrope-almandine.

Localities

India, USA, Brazil

Occurance

Metamorphic rocks