Introduction to Tridacna Pearls

What are Tridacna Pearls?

Like nacreous pearls, tridacna pearls grow in mollusks. Specifically, they form in bivalve mollusks of the Tridacna genus of clams. This genus includes giant clams of enormous size. In fact, the largest pearls ever found from this genus are weighed in kilograms rather than carats.

However, these aren’t “true” pearls. Technically, tridacna pearls are calcareous concretions because they aren’t made of nacre. In a tridacna pearl, instead of forming in sheets, the mineral aragonite arranges itself radially. In a fine specimen, this results in an exciting flame structure that rolls across the gem.

These clams grow in tropical reefs in the Indo-Pacific region, primarily in Indonesia and the Philippines. If you’re on a tridacna pearl buying trip in these island nations, keep an ear open for “kima,” the Indonesian word for these pearls.

Tridacna Pearl Quality Factors

The four Cs of colored gemstone grading aren’t the best way to evaluate either nacreous or non-nacreous pearl quality. Instead, the calcareous concretion’s flame structure, color, luster, shape/symmetry, texture, and size determine quality.

Flame Structure

In a clam pearl, the flame structure is the most important value factor. This phenomenon is similar to chatoyancy, with flames…

Addison Rice

A geologist, environmental engineer and Caltech graduate, Addison's interest in the mesmerizing and beautiful results of earth's geological processes began in her elementary school's environmental club. When she isn't writing about gems and minerals, Addison spends winters studying ancient climates in Iceland and summers hiking the Colorado Rockies.

View All Articles