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— Typically in regionally metamorphosed igneous and sedimentary rocks, as well as in contact metamorphosed calcium-rich sediments; an alteration product of plagioclase feldspars (Anthony et al., 2001—2005). Faceted specimens are extremely rare.

Specimen figured

Clinozoisite — specimen 0047weight: 0.57 ct; shape: oval. Very clean specimen; good mixed style cut. Source: David Weinberg, Multicolour Gems Ltd.


The section ‘Classification’ presents descriptions of 171 different kinds of natural gemstones (106 mineral species). The Nickel-Strunz systematic order (10th edition) is used. Specimens of the classes shown below are currently available. Since gemmology does not always follow the systematics of minerals in naming, many popular varieties or just ’names’ are also listed.

Classes after Nickel-Strunz

1. Elements
2. Sulphides & sulphosalts
3. Halides
4. Oxides & hydroxides
5. Carbonates (Nitrates)
6. Borates
7. Sulphates
8. Phosphates, arsenates, vanadates
9. Silicates


— In gneisses, schists, included pegmatites, and quartz veins, from regional metamorphism of sedimentary rocks (Anthony et al., 2001—2005).

Specimen figured

Kyanite — specimen 0481weight: 0.59 ct; shape: oval. Clean specimen; mixed style cut; good polish.
Kyanite — specimen 0481