WorldWide Drilling Resource

June Birthstone is Pearl by Harry W. Short, Engineering Geologist Pearl, the June birthstone, is a hard, white, round object valued as a gemstone for use in jewelry. Its value in jewelry is determined by a combination of luster, color, size, lack of surface flaws, and symmetry, which is appropriate considering the type of pearl. Not mined, pearls form inside the shells of oysters in response to irritation from objects such as sand grains inside their shells. Layers in the pearl are the minerals aragonite or calcite. The calcium carbonate (CaCO 3 ) in the two minerals is held together by an organic compound named conchiolin , often called narce , meaning mother of pearl . The unique luster of pearls depends upon the reflection and refraction of light from their translucent layers. The iridescence some pearls display is caused by the overlapping of successive layers which break up light falling on the surface. Pearls are usually white, sometimes with a creamy or pinkish tinge, but may be tinted yellow, green, blue, brown, purple, or black. Black Tahitian Pearls are highly valued because of their rarity. The culturing process for black pearls produces a smaller number since they are often rejected by the host oyster. Before the 20th century, divers pulled oysters from ocean floors and river bot- toms and checked each individually for pearls. Only three or four oysters in three tons produce perfect pearls. Now, almost all pearls used for jewelry are cultured by planting a core or nucleus into pearl-producing oysters. Pearls are usually harvested three years after plant- ing, but it can take six years or longer before a pearl is produced. Pearls come in eight basic shapes: round, semi-round, button, drop, pear, oval, baroque, and ringed. Perfectly round pearls are the rarest, highly valued, ex- pensive, and are generally used in neck- laces or in strings of pearls. Irregular and button pearls find use in necklaces. Pear-shaped pearls are sometimes referred to as teardrop pearls and are most often seen in earrings, pendants, or as a center pearl in necklaces. Baroque pearls have a different appeal than the more standard shapes; they are often highly irregular and make unique and in- teresting shapes. Ringed pearls are char- acterized by concentric ridges, or rings, around the body of the pearl. Minnie Pearl is not included herein since she was a Grand Ole Opry star. Harry In memory of Harry Short. His articles will continue posthumously. Contact: michele@ worldwidedrillingresource.com 67 WorldWide Drilling Resource ® JUNE 2016