Amethyst Identification Sheet

The purple quartz that has captivated collectors and jewelers for millennia — and fades if you leave it on the windowsill.

For: Collectors, Lapidary Artists, Students

Mohs hardness 7

Streak White

Luster Vitreous Vitreous (glassy)

CleavageNone — conchoidal fracture; same as all quartz varieties

Crystal habit Prismatic, Pyramidal, Drusy Six-sided prism ending in a six-sided pyramid; often in drusy clusters; color concentrated near terminations

Amethyst is a variety of quartz whose purple color comes from iron impurities combined with natural irradiation deep in the crystal lattice. It forms the same hexagonal prisms with pyramidal terminations as colorless quartz but ranges from pale lilac to deep violet. The purple coloration is its defining field feature — but note that color is not uniformly distributed; most crystals show patches or zones of color concentration near the tips. Extended exposure to bright sunlight fades amethyst significantly, so store display specimens away from windows. Heat treatment above 400°C turns amethyst yellow-orange, producing the citrine sold at many gem shows.

Common lookalikes

Purple fluorite (softer at 4, octahedral cleavage); purple tourmaline (striated crystals, different system); synthetic amethyst (available and difficult to distinguish without lab testing). Color zoning concentrated at tips is a good indicator of natural origin.