mineral

Amethyst Geode (polished heart-cut)

Silicon Dioxide (SiO2) with iron impurities

Hardness: 7 (Mohs scale); Color: Pale purple to deep violet; Luster: Vitreous (glassy); Crystal Structure: Hexagonal (trigonal); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 (Mohs scale)
Color: Pale purple to deep violet
Luster: Vitreous (glassy)

Identified March 18, 2026More mineral →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 7 (Mohs scale); Color: Pale purple to deep violet; Luster: Vitreous (glassy); Crystal Structure: Hexagonal (trigonal); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed within gas bubbles (vesicles) in volcanic basalt. As mineral-rich groundwater seeped into these cavities over millions of years, silica precipitated to form crystals. The purple color is caused by irradiation of trivalent iron impurities. These specimens often date to the Cretaceous period (~100-140 million years ago).

Uses & applications

Primarily used as decorative display pieces, for metaphysical/lapidary collecting, and high-quality crystals are faceted for jewelry. Smaller fragments or lower quality stones are used in industrial abrasives.

Geological facts

Amethyst is the birthstone for February. The name comes from the Greek word 'amethystos', meaning 'not intoxicated', as ancient Greeks believed it could prevent drunkenness. These large geodes are famously sourced from the Paraná Basin in South America.

Field identification & locations

Identify in the field by looking for dull or rough basaltic rocks that feel surprisingly light or sound hollow when tapped. Common locations include Rio Grande do Sul (Brazil) and Artigas (Uruguay). Collectors should look for deep purple saturation, large crystal points, and a lack of visible repairs on the host rock.

Other mineral specimens

See all

Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

Epidote

Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)

metamorphic

Nephrite Jade

Nephrite

Mineral/Rock

Banded Gneiss (River Rock/Pebble)

Gneiss (specifically a banded variety often found as a river rock)

Metamorphic Rock

Green Apatite on Albite

Fluorapatite [Ca5(PO4)3F] on Albite [Na(AlSi3O8)]

mineral

Epidote

Epidote - Ca2(Al2,Fe3+)3(SiO4)3(OH)

mineral