Pearl

Hardness: 2.5-4.5 (Mohs scale), relatively soft. Color: White, cream, pink, silver, black, peacock, blue, green, and yellow are common, often with iridescent overtones (orient). Luster: Pearly (iridescent). Crystal Structure: Amorphous (no true crystalline structure), but composed of microscopic crystalline layers of aragonite or calcite. Cleavage: None. Specific Gravity: 2.60-2.85.

Pearls are organic gemstones produced within the soft tissue of a living shelled mollusk (e.g., oysters, mussels). They form when an irritant (such as a parasite or a piece of shell) gets inside the mollusk, and as a defense mechanism, the mollusk secretes layers of nacre (calcium carbonate and conchiolin) around the irritant, gradually building up the pearl. The formation process can take several years. There is no specific geological age as they form continuously in living organisms.

Pearls are primarily used in jewelry (necklaces, earrings, rings, bracelets) due to their unique luster and beauty. They have been prized as gemstones for millennia. Less commonly, very small or imperfect pearls can be ground into powder for cosmetics or traditional medicine, though this is rare for gem-quality pearls.

Natural pearls are extremely rare and highly valued; most pearls used in jewelry today are cultured, meaning an irritant (a bead or piece of tissue) is intentionally inserted into the mollusk by humans to stimulate pearl formation. The value of a pearl is determined by its size, shape (round being most valuable), color, luster, surface quality, and nacre thickness. Freshwater pearls tend to be more abundant and varied in shape and color than saltwater pearls. The 'orient' of a pearl refers to the iridescent play of colors that shimmers on or just below the surface.

In the field (or when examining a specimen, as pearls are not found like rocks in the ground), pearls are identified by their characteristic pearly luster, typical shapes (spherical, oval, baroque), and often a slightly gritty feel if rubbed gently against a tooth (though this test can damage the pearl). They are commonly found in commercial pearl farms for cultured pearls, or historically, in mollusk beds in various oceans and freshwater bodies. Tips for collectors: Authenticate pearls carefully, distinguishing natural from cultured and imitation pearls. Look for good luster and minimal surface blemishes. Size and shape uniformity are key for strands of pearls.