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What is Spiny Oyster?

The material called, “Spiny Oyster,” used by Native American artists to make inlays in fine jewelry, comes from the shell of the bivalve mollusk, Spondylus varius. The genus’ scientific name, “Spondylus,” means “spines on its back.” Aside from its scientific name, it’s also known as Thorny Oyster, Spiny Oyster, Spondylus, and Spondylid.S4 The bivalve mollusks include the clams, oysters, cockles, mussels, and scallops and include both saltwater and freshwater species. Like many other bivalve mollusks, the soft, meaty interior of Spondylus is edible, so the Spiny Oyster’s valued for its hard, outer shell as well as its interior meat. Despite its name, the Spiny Oyster’s much more closely related to the scallop than to the true oyster.S5

The shell’s made up of several parts, and the portion used to make inlays is known as Aragonite, which consists of the carbonate mineral, calcium carbonate (CaCO3). Aragonite has the same chemical formula as calcite, but it’s formed by biological and physical processes in marine and freshwater environments.

The crystal lattice of aragonite varies from that of calcite.G13 Looking at smooth, polished Spiny Oyster set in a ring next to turquoise, one sees a very smooth, polished orange or red surface. However, the crystal shape of this mineral actually consists of an orthorhombic system (having three unequal axes at right angles to each other) with needle-like (acicular) crystals, giving it a spiny, branched appearance, unlike the blocky appearance of calcite.

Living Spondylus shells are, indeed, very spiny, but the polished product looks very smooth, with some of its color variation strongly resembling that of the Blood Oyster. The resemblance is strong enough that it’s important to ask, when purchasing these materials, if they’re from Blood Oyster or Spiny Oyster. Artists often use Spiny Oyster as a substitute for Blood Coral. Although not nearly as rare as the Blood Coral or Rose Coral, divers collect Spiny Oyster by hand, making the work laborious and relatively expensive, with some risks.N18

The most commonly used Spondylid Bivalve shell colors include orange, reds, and purples and may include distinct striations and color variations. One also finds pink, red, brown, yellow, orange, and white on the market. The Yellow Spiny Oyster’s especially rare.

In the American Oceans, the Spondylids occur along the North American coasts, as far north as North Carolina, on the Atlantic Coast, and northwestern Mexico, on the Pacific Coast. It develops in waters to South America. The Orange Spiny Oyster occurs in shallow to moderately deep waters, where snorkelers and scuba divers readily harvest them. Purple Spiny Oysters grow in deeper water, making them more difficult to find and harvest. Their color varies from purple through pink.G12

Contributing Author – Jeffery Bacon

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