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— An uncommon accessory mineral in granite pegmatites (Anthony et al., 2001—2005). Faceted specimens are very rare. The largest faceted stone is a 40.2 carat (Arem, 1987: 109).

Specimen figured

Hambergite — specimen 0499weight: 0.34 ct; shape: oval. Very clean specimen; very good mixed cut style. 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


— Produced by regional or contact metamorphism of magnesium carbonate, mafic, or ultramafic rocks (Anthony et al., 2001—2005). Faceted specimens are extremely rare.

Specimen figured

Actinolite — specimen 0075weight: 1.48 ct; shape: oval. Very clean specimen; mixed style cut; good polish. Source: John Bradshaw, Coast to Coast Rare Stones International.
Actinolite — specimen 0075