The majority of gemstones, such as diamonds and sapphires, are minerals. They’re inorganic pieces born from geological activity. Jewels such as mother of pearl stand apart this organic gem comes from animals. Mother of pearl, also known as nacre, is taken from shells. What makes mother of pearl stand out from other mollusks is its nacreous sheen, also called iridescence. Multiple species produce this gem, including those farmed for pearls.
Animals and pearls
Freshwater pearl mussels, as well as members of the Pinctada genus, create both pearls and nacre. While abalone also creates pearls, it’s more valued for its meat and shells. In the early twentieth century, top and turban snails too were sought out for mother of pearl.
All of these creatures produce nacre from their mantles, or body walls. Mother of pearl is constantly formed and settles on the animal’s inner shell. If an irritant appears inside the body, nacre encases the foreign object, creating a pearl. Should this happen against the shell, a blister pearl, or fusion of pearl and nacre, is born.
Due to the variables between species, some details vary. Mother of pearl has a Mohs hardness between 2.5 and 4.5. Any stone of similar or greater hardness is able to scratch it. Nacre is also quite tough, or resistant to blows, comparable to silicon. The jewel’s specific gravity ranges from 2.65 to 2.87 times the equivalent amount of water.
The jewel is made of two substances, aragonite and conchiolin. Aragonite is a type of calcium carbonate in the form of hexagonal platelets. They’re ten to twenty micrometers wide, smaller than a strand of hair. Aragonite settles one atop the other in a brick pattern glued together by conchiolin, a complex protein.
Between the arrangement of platelets and aragonite’s thickness, light faces interference. It scatters and reflects at different angles and speeds. This creates structural color, formed from light rather than pigment. With nacre, iridescence, a form of structural color, appears.
Nacre is available in a rainbow of natural colors. In addition to neutral white, black and grey, pink, blue-green and more are also possible. Variations include banded hues and even cat’s eye effects. While mother of pearl has a beautiful sheen, the gem itself is opaque.