GEM KNOWLEDGE · LABORATORY NOTES
Purple Anhydrite
The purple portion of this Chinese palm stone was identified as anhydrite, accompanied by calcite and phlogopite.
The tested identification: The purple portion of this Chinese palm stone was identified as anhydrite, accompanied by calcite and phlogopite.
The tested palm stone was reported from China. The laboratory describes its purple portion as anhydrite with elevated strontium. The pink portion is magnesium-bearing calcite, and the black mica is phlogopite. Its olive-green phase was not conclusively identified; the report discusses a possible amphibole and calls for more study.
Anhydrite (CaSO₄) and gypsum (CaSO₄·2H₂O) are distinct minerals. Selenite is a variety of gypsum. “Angelite” is a gem trade term for a blue gray anhydrite material from Peru, rather than a separate mineral species. This Chinese purple specimen is accurately identified by its test as anhydrite.
Related names: Purple Anhydrite · Purple Angelite · Purple Selenite
Angelite trade name · Anhydrite · Gypsum
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Analytical Result Report Sample id: 9252 (Purple palm) Submitted by: K. Bitner Date submitted: Jan. 15, 2021. Date completed: Jan. 27, 2021. Operating conditions: JEOL JSM-6400 operated at 25 kV acceleration potential, 15 mm working distance, 15 degrees sample tilt, coated with 250 Å carbon. Using the X-ray fluorescence attachment with 35kv potental in conjunction with the EDS system. Fig. 1: Photograph of the specimen, approximately 45x44x20 mm. Table 1: Compositions of the specimen (In weight percent) element purple Olive green pink black Silicon dioxide 0.15 55.92 0.37 41.11 Aluminum oxide nd 7.18 0.23 11.77 Calcium oxide 39.5 14.42 48.22 0.22 Magnesium oxide 0.1 20.52 3.11 25.88 Sulfur trioxide 57.9 0.12 0.11 0.14 Iron oxide 0.02 2.49 0.27 3.12 Strontium oxide 0.66 nd 0.13 0.04 Titanium oxide nd 0.18 nd 0.65 Manganese oxide nd nd 0.33 0.08 Potassium oxide nd 0.11 nd 11.09 Vanadium oxide nd nd nd 0.03 Chlorine nd 0.31 nd nd Summary of findings: This is a very unusual specimen (Fig. 1)! The light purple material is anhydrite (Table 1). The strontium content is elevated which is interesting. The olive-green material is problematic, it looks a lot like an epidote group mineral visually but the high magnesium content is a problem, optically is not a good match either. Rather, it could be an amphibole group member such as something between pargasite/tremolite. This mineral needs more scrutiny. Chlorine is notable (Table 1), another link to an original evaporite origin. The pink material is a carbonate, essentially a calcite with magnesium as the man substituting element and lesser amounts of iron and manganese (Table 1). The black mica is phlogopite. Magnesium is dominant over iron (Table 1), interesting to note a little vanadium is present. The origin of this material may be a result of skarn formation of an original evaporite-rich sedimentary sequence in proximity or contact with an igneous intrusion or under strong tectonic conditions at depth. Date: January 27, 2021 Signature