mineral (biogenic silica/calcium carbonate substrate)
Shell Cameo (Sardonyx Shell)
Cassis madagascariensis (Sardonyx shell)
Hardness: 3-4 (Mohs scale), Color: Creamy white carving over a brownish-orange background, Luster: Vitreous to waxy, Structure: Organic calcium carbonate (Aragonite/Calcite layers), Cleavage: None
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Physical properties
Hardness: 3-4 (Mohs scale), Color: Creamy white carving over a brownish-orange background, Luster: Vitreous to waxy, Structure: Organic calcium carbonate (Aragonite/Calcite layers), Cleavage: None
Formation & geological history
Formed through biogenic processes in marine mollusks; the shell grows in distinct colored layers that artists exploit for relief carving. Most modern high-quality shells are sourced from the Caribbean or Indian Ocean.
Uses & applications
Primarily used in fine jewelry (brooches, rings, pendants) and as decorative miniature art. It is a classic Victorian-style collectible.
Geological facts
Cameos have been carved since ancient times, but the shell variety became highly popular during the Victorian era. The 'Sardonyx' shell is specifically prized for its deep chocolate or reddish-orange ground which mimics the look of the more expensive sardonyx gemstone.
Field identification & locations
Identify by looking for distinct layers of color. When viewed under magnification, an authentic hand-carved shell cameo will show tiny chisel marks and slight imperfections, unlike molded plastic or resin imitations which are perfectly smooth.
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