The author recently examined a group of dark-colored pearls reportedly produced by an Atrina-species mollusk from the Pinnidae family (known as “pen pearls”). The majority of pen pearls have nacreous surfaces and display characteristic linear-looking nacre under high magnification (N. Sturman et al., “Observations on pearls reportedly from the Pinnidae family (pen pearls),” Fall 2014 G&G, pp. 202–215). Some of the pearls examined in the group exhibited a near-colorless translucent frosted surface on certain areas. This structure is seldom observed on nacreous pearls from other mollusk species. Raman spectroscopy using 514 nm laser excitation revealed that the areas were composed of aragonite. A 0.62 ct dark brown pearl displayed the most interesting surface, composed of layered aragonite crystals in various sizes, resembling ice on a frozen river (see above).
The author recently examined a group of dark-colored pearls reportedly produced by an Atrina-species mollusk from the Pinnidae family (known as “pen pearls”). The majority of pen pearls have nacreous surfaces and display characteristic linear-looking nacre under high magnification (N. Sturman et al., “Observations on pearls reportedly from the Pinnidae family (pen pearls),” Fall 2014 G&G, pp. 202–215). Some of the pearls examined in the group exhibited a near-colorless translucent frosted surface on certain areas. This structure is seldom observed on nacreous pearls from other mollusk species. Raman spectroscopy using 514 nm laser excitation revealed that the areas were composed of aragonite. A 0.62 ct dark brown pearl displayed the most interesting surface, composed of layered aragonite crystals in various sizes, resembling ice on a frozen river (see above).
