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"Fluorine-Chrysoprase" - a deceptive trade name

A green rock was submitted to the EPI laboratory, declared as 'Fluorine-Chrysoprase'. According to the rules of mineralogical nomenclature, 'Fluorine-Chrysoprase' should be a chalcedony containing nickel (= Chrysoprase) and fluorine.

Under the microscope the expected fibrous structure of a chalcedony did not show up. Pronounced cracks indicated a very very good cleavage. In addition the density of 2.9 - 3.1 did not fit on Chrysoprase. On a cut and polished surface the refracive index could be determined with 1.45, a value which can clearly be assigned to fluorite.

To determine the exact mineral composition and element content, a mineralogical thin section was made and an X-ray fluorescence analysis (XRF) was carried out. The thin section analysis clearly showed that apart from fluorite and the remains of decomposed feldspars, only coarsely crystallised quartz - but no chalcedony - was present. The element analysis (XRF) did not show a measurable content of nickel.

Fluorites in such a coarse formation as in the analysed rock are often very hydrous and are called Hydrofluorite.

According to these analysis results, the designation "Fluorine-chrysoprase" has to be classified as misleading. The correct name is (Hydro-) fluorite.