Gem Minerals
Garnet
What it is
A family of nesosilicate minerals that all share the same crystal structure but vary widely in chemistry and color. Almandine is deep red, grossular ranges from green to orange, and spessartine is vivid orange. Garnets are so hard and uniform they're used as industrial abrasives.
How it forms
Forms in metamorphic rocks under high temperature and pressure. Garnet is an index mineral in petrology — its presence and composition tell geologists exactly what conditions a rock experienced.
X₃Y₂(SiO₄)₃ — variable X and Y cations
