mineral

Spiny Oyster Shell

Spondylus varians (Biogenic Calcium Carbonate)

Hardness: 3.5-4.0 (Mohs); Color: Orange, red, purple, and yellow; Luster: Pearly to vitreous when polished; Structure: Amorphous biogenic layers; Specific Gravity: 2.7-2.9

Hardness: 3
Color: Orange, red, purple, and yellow
Luster: Pearly to vitreous when polished

Identified May 9, 2026More mineral →

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Physical properties

Hardness: 3.5-4.0 (Mohs); Color: Orange, red, purple, and yellow; Luster: Pearly to vitreous when polished; Structure: Amorphous biogenic layers; Specific Gravity: 2.7-2.9

Formation & geological history

Formed through biogenic processes by bivalve mollusks in tropical marine environments, typically found attached to coral reefs and rocks in the warm waters of the Sea of Cortez and the Pacific Ocean.

Uses & applications

Primarily used in jewelry making, particularly in Native American (Navajo, Zuni, and Santo Domingo) turquoise inlay work, bead making, and lapidary arts.

Geological facts

Spiny Oyster is not a true oyster but a 'spondylus.' It has been used for thousands of years as a trade commodity and ritual object by Pre-Columbian cultures including the Aztecs and Incas.

Field identification & locations

Identify in the field by its distinct spiny exterior when raw and layered white/colored banding when cut. Commonly found in Southwestern jewelry markets. Collectors look for vibrant, uniform colors without excessive pit holes.

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