Silicates: Garnet

Composition: X₃Y₂(SiO₄)₃; where X may be Mg (pyrope), Fe (almandine) or Mn (spessartine) with Y predominantly Al, or X may be Ca with Y predominantly Al (grossular), Fe (andradite) or Cr (uvarovite)

Crystal system: Isometric; crystals characteristically dodecahedral, also massive and granular forms

5.11.1
spessartine garnet crystals

Properties:

• Vitreous lustre
• Variable color; dark red to brown and yellowish green to dark green most common
• White to pale brown or green streak
• Knife does not scratch (Mohs Hardness 6-7.5)
• Above average to high density depending on composition
• No cleavage
• Smooth to uneven fracture
• Not ferromagnetic
• Does not react with hydrochloric acid (HCl)

Occurrence:

Garnets occur in regional and contact metamorphic rocks, some felsic igneous rocks and also in heavy mineral sand and gravel deposits.

5.11.2 spessartine garnet crystals	5.11.3 andradite garnet crystals King Island Australia

5.11.4 andradite garnet crystals King Island Australia	5.11.5 andradite garnet crystals King Island Australia

Garnet has local use as an abrasive material and is also a gemstone when sufficiently flawless and of good color.