Almandine

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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

Oval, faceted Almandine garnet

Color

Brownish red, red to violet/purple

Spectroscope

Almandine has a typical iron spectrum

Almandine spectrum.jpg

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

Almandine sinks in all common heavy liquids.

Optical effects

Almandine may show asterism and chatoyancy

Varieties

Rhodolite

Faceted Rhodolite Garnet
Photo courtesy of Rick Martin

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

Inclusions

Silk, crystals, and a crystal looking like a skull, inside of a pyrope-almandine garnet.
~85X Magnification
©Jamey Swisher


Localities

India, USA, Brazil

Occurrence

Metamorphic rocks