Star Rhodochrosite
The Carlsbad laboratory received a 19.44 ct semitransparent orangy pink round cabochon for identification (figure 1). With the unaided eye, a four-rayed star could be seen across the dome. Standard gemological properties, including a refractive index of 1.68–1.58 with a birefringence blink and a specific gravity of 3.71, were documented and consistent with the gem species rhodochrosite.
Asterism is created when light is reflected off well-aligned inclusions and returns as a star across the surface of the stone. Such stones are commonly cut as cabochons to properly display this phenomenon. The asterism seen in this rhodochrosite was created from fluid inclusions that run parallel to the base of the cabochon (figure 2). The fluid inclusions were rhomboid in shape, which caused the star to have four rays. It is worth noting that the rays of the star did not cross perpendicular to each other, and this is due to the rhomboid fluid inclusions intersecting at an angle not at 90°.
Many gemstone species display asterism, but this was the author’s first opportunity to see a star rhodochrosite. This 19.44 ct stone is a perfect example of why one should always keep an eye out for the unexpected.
