Garnets are silicate minerals that occur in nearly every color, with red (almandine and pyrope) being most common in the field. They appear as well-formed dodecahedral or trapezohederal crystals embedded in schists and gneisses, often popping out as rounded, pitted grains in stream gravels. The combination of vitreous to resinous luster, hardness above 6.5, and distinctive 12-sided crystal form makes garnet one of the more satisfying field identifications. A neodymium magnet attracts many garnets due to iron content — a useful supplementary check.
Garnet Group Identification Sheet
Not one mineral but a family — hard, dense, and found in almost every metamorphic rock Rockies encounter.
Streak
White
Luster
Vitreous, Resinous, Subadamantine
Vitreous to resinous; subadamantine in polished gem material
CleavageIndistinct; fracture conchoidal to uneven — produces rounded, irregular fragments
Crystal habit
Dodecahedral, Trapezohedral, Granular
Rhombic dodecahedron or trapezohedron; commonly found as rounded grains in stream gravels
Common lookalikes
Red glass (softer, no crystal form); spinel (octahedral cleavage, different crystal system); ruby (hexagonal, harder). Test: 12-sided crystal form in schist is nearly diagnostic; check with a magnet for iron-bearing varieties.