mineral

Amethyst Geode Cathedral

Amethyst (Silicon Dioxide - SiO2 with Iron impurities)

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

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

Identified March 18, 2026More mineral →

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Physical properties

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

Formation & geological history

Formed in gas cavities (vesicles) within volcanic lava flows. As the lava cools, mineral-rich water seeps into these cavities, precipitating quartz crystals over millions of years. Most large cathedrals date to the Cretaceous period.

Uses & applications

Primarily used as decorative home decor, in feng shui practices, and as high-end metaphysical or collector specimens. Smaller fragments are faceted for jewelry.

Geological facts

The purple color is caused by irradiation of iron impurities within the quartz. The exterior 'rind' of these geodes is typically composed of basalt and a layer of chalcedony/agate.

Field identification & locations

Identify by purple hexagonal crystal points inside a hollow rock cavity. Commonly found in the Rio Grande do Sul region of Brazil and Artigas, Uruguay. Collectors look for deep 'grape' purple color and intact crystal terminations.

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