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— A common accessory mineral in igneous rocks, anorthosite, and granite pegmatites; in hydrothermally-altered rocks; in gneiss, schist, contact metamorphosed limestones; in clays, shales (Anthony et al., 2001—2005). Faceted specimens are very rare.

Specimen figured

Rutile — specimen 0173weight: 0.97 ct; shape: octagon. Very clean specimen; good step cut style. Source: John Bradshaw, Coast to Coast Rare Stones International.


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


— Most common in felsic volcanic rocks; in volcanic glass; also from mafic, high-temperature contact metamorphic, and hydrothermally altered rocks; from eclogite nodules in kimberlite (Anthony et al., 2001—2005).

Specimen figured

Sanidine — specimen 0017weight: 1.08 ct; shape: oval. Very clean specimen; very good mixed style cut. Source: John Bradshaw, Coast to Coast Rare Stones International.
Sanidine — specimen 0017