Conch pearls are composed of tightly packed calcium carbonate crystals in the forms of aragonite and calcite, held together by other organic matter and a small amount of water. Unlike traditional pearls, conch pearls are not composed of nacre. They are classified as non-nacreous calcareous concretions, and are formed deep within the mantle tissue of the conch.

Although conch pearls don’t form in the layered, nacreous structure typical of traditional pearls, they can still display internal banding. These bands may look like growth rings, and in a structural sense, they are. But they form through fibrous aragonite crystals arranged in a lamellar, crossed-lamellar pattern—not through stacked nacre platelets. In nacre, shimmer comes from light interference between tightly packed aragonite layers held together by conchiolin. In conch pearls, the flame effect comes from light scattering across aligned crystal fibers just beneath the surface.

Sectioned conch pearl showing internal banding caused by fibrous, lamellar crystal growth.

Conch pearls usually form due to displaced tissue or abnormal cell growth, without the typical pearl sac, nacreous layers, or a nucleus. Aragonite crystals grow in a lamellar pattern, rather than stacking in concentric layers as seen in nacreous pearls. Under magnification, this structure has a sort of fibrous or flaky appearance. Viewed under polarized light or through X-ray diffraction, the aragonite crystals show a parallel orientation.

The refractive index of conch pearls averages around 1.51, and specific gravity is typically around 2.85—both values consistent with a mixture of aragonite and calcite. Gemological labs identify conch pearls through a combination of visual inspection, refractometry, and Raman spectroscopy. The absence of nacre, the presence of aragonite, and the internal growth pattern confirm identity.

Not all conch pearls display eye-visible flame. In some cases, faint flame is only visible under 10x magnification. When present, flame is a key indicator of authenticity.

Natural conch pearls showing typical color and shape variation. Some display visible flame, while others appear smooth and porcelain-like.