Fossilized shell consisting of Emerald
Eleven semitranslucent to opaque green and brown fossilized shells. Most of these specimens show clear shell outlines with green emerald grains. Photo by Johnny Leung.
Fossilized shells can be replaced by various types of gemstones, such as quartz and chalcedony (Spring 2014 Gem News International, p. 77), opal (A. Cody and D. Cody, The Opal Story: A Guidebook, Melbourne, 2008), and demantoid garnet (Winter 2013 Gem News International, pp. 257–258). In rare cases, emerald may also participate in the petrification of the shell and form pseudomorphs.
Recently, the Hong Kong laboratory received 11 fossilized shells composed primarily of emerald, measuring 13.00 × 8.20 × 6.16 mm to 24.54 × 16.72 × 12.57 mm and weighing 3.22 to 20.63 ct (figure 1). Most of them preserved the distinctive gastropod shell outlines, with different degrees of weathering.
Under magnification, numerous small light green to green anhedral emerald crystals contained very fine fluid inclusions associated with well-formed brassy pyrite grains (figure 2), which is one of the most common mineral inclusions in Colombian emeralds (S. Saeseaw et al., “Geographic origin determination of emerald,” Winter 2019 G&G, pp. 614–646).
An X-ray radiograph further revealed the spiral skeleton of the shell and scattered pyrite crystals (figure 3). The polycrystalline emerald was deposited evenly throughout the specimens, indicating complete replacement.
Read entire article here: https://www.gia.edu/gems-gemology/fall-2021-fossilized-shell-emerald?utm_source=Knowledge-Rocks&utm_medium=email&utm_campaign=2021-12-08&mkt_tok=ODQ1LVdFTS02MzYAAAGBOcIPbDI3Cls1nBPpV3Lmycy6UZgtwvaxHGjm0VhJyj4qgsE1RSQji4Ad8-soElvwFqWrMdCXoUHwEsQb3Bp6S5jRHJeV6jNaU0ZmaoAt