Garnet Group (cubic) M32+R23+[SiO4]3; M2+= Mg,Fe2+, Mn2+, Ca; R3+= Al,Fe3+, Cr3+

Garnet 1P
  • Pyrope
  • Almandine Fe32+Al2[SiO4]3
  • Spessartine
  • Grossular Ca3Al2[SiO4]3
  • Andradite
  • Uvarovite
Colour: colourless, it may be pink, yellow, brown (Garnets content Fe, Mn, Ti)
Pleochroism: non pleochroic
Habit: commonly euhedral forms
Relief: high
Cleavage, fracture: none, show irregular fractures
Garnet PX
 Isotrophic. Therefore it doesn't prove crossed polarised light properties.

Olivines (orthorhombic) (Mg2,Fe22+)SiO4

Olivine 1P
  • Forsterite Mg2[SiO4]
  • Fayalite Fe2[SiO4]

Colour: colourless, Olivines content Fe may be coloured
Pleochroism: non pleochroic, Olivines content Fe may be slightly pleochroic
Habit: usually anhedral crystals, ocasionally euhedral tabular forms
Relief: high
Cleavage, fracture: none, show irregular fractures
Alternations: Serpentine is common alternation of Olivine. Usually altering Olivine grain is surrounded by black smudge in 1P and PX

Olivine PX
 Isotropic or anisotropic: anisotropic
Extinction: straight
Interference colours: 2nd order

Zircon (tetragonal) ZrSiO4

Zircon 1P
 Colour: colourless
Pleochroism: non pleochroic
Habit: tabular or square shaped cross section
Relief: high
Cleavage, fracture: none
Inclusions: inclusions in Biotite and Muscovite
Zircon P X
 Isotropic or anisotropic: anisotropic
Extinction: straight
Interference colours: 3rd order

Titanite (monoclinic) (Ca,Ti)[O/SiO4]

Titanite 1P
 Colour: colourless, light brown
Pleochroism: non to weakly pleochroic
Habit: typical double wedge or diamond shape
Relief: high
Cleavage, fracture: good cleavage, show irregular fractures
Titanite PX
 Isotropic or anisotropic: anisotropic
Extinction: inclined
Interference colours: 3rd order
Last modified: Monday, 3 April 2017, 10:51 AM