Pearls are one few popular gemstones that aren’t minerals, in other words it’s an organic substance produced by living being. Other examples include amber, coral, jet, and ivory. Pearls however are unique in that they come out of the shell completely finished, no polishing or carving necessary.
One interesting variation occurs when different types of material intertwine within the same pearl. There are basically two substances that constitute pearls. Nacreous pearls are the ones you’re probably more familiar with, they’re made of the lustrous nacre material called aragonite. The other type, non-nacreous pearls, are made of a harder, duller material called calcite. When you’re eating an oyester and discover a small flaky bit of mineral inside – that’s a calcite pearl.
However when the two substrates intermingle, really interesting pearls can result. These are the so called “flame pearls” that display mesmerizing patterns of lustrous nacre, resembling gas nebulae in space, the delicate pattern of an iris, and of course the branching fingers of a flame. Examples like the one above are highly prized for their symmetry and evenness of pattern.
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