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— In pegmatites, greisens, and alpine and hydrothermal veins (Anthony et al., 2001—2005).

Specimen figured

Phenakite — specimen 0492weight: 0.64 ct; shape: oval. Very clean specimen; very good Portuguese 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


— Primarily in cavities in basalts; in gneisses and amphibolites, and in dikes derived from syenitic magmas (Anthony et al., 2001—2005). Extreme rarity as faceted specimens.

Specimen figured

Scolecite — specimen 0068weight: 0.54 ct; shape: octagon. Very clean specimen; step cut style; good polish. Source: John Bradshaw, Coast to Coast Rare Stones International.
Scolecite — specimen 0068