Micro-World Gems & Gemology, Fall 2024, Vol. 60, No. 3

Hedenbergite in Quartz

Liyan He and Wingtak Lui

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Figure 1. These dark green acicular aggregates in quartz were identified as hedenbergite. Photomicrographs by Liyan He; fields of view 9.20 mm (left) and 8.30 mm (right).
 
Figure 1. These dark green acicular aggregates in quartz were identified as hedenbergite. Photomicrographs by Liyan He; fields of view 9.20 mm (left) and 8.30 mm (right).

Quartz is known to host a wide variety of inclusions. In a large group of polished quartz samples recently examined, the authors observed groups of dark crystal inclusions that took the shape of a sea urchin. In some samples where the dark crystal reached the surface, the cross section of the crystal habit was rhomboid, indicating they were monoclinic. Under magnification, the inclusions were transparent to translucent and dark green to brownish green (figure 1). Raman spectra identified the inclusions as hedenbergite, confirmed by comparison with the RRUFF database. Hedenbergite, CaFe2+Si2O6, is a member of the pyroxene group. Based on previous work (Winter 2023 G&G Micro-World, pp. 503–504), we realized that the material known in the trade as “urchin quartz” might contain inclusions other than hollandite.

Figure 2. A sphalerite crystal in quartz. Photomicrograph by Liyan He; field of view 11.40 mm.
 
Figure 2. A sphalerite crystal in quartz. Photomicrograph by Liyan He; field of view 11.40 mm.

In the samples that contained hedenbergite, we also identified a translucent yellow to light brown inclusion in these samples (figure 2). The crystal was identified by Raman spectroscopy as sphalerite, consistent with the RRUFF database.

Liyan He is affiliated with the Guangdong Gemstones & Precious Metals Testing Center in Guangzhou, China. Wingtak Liu is affiliated with Min De Minerals & Gem Research Co., Ltd., in Nanjing, China.