Lapis lazuli
from the Antique Jewelry University
Lapis lazuli is a rock aggregate made up from - predominantly - the minerals lazurite, sodalite, nosalite and hauyne. It has a typical cobalt blue color, often with patches of pyrite (golden) and/ or calcite (white). It was this rock which was powdered to create the ultramarine pigment used by painters prior to the 19th century[1]. Historically this gemstone comes from Afghanistan and this location was reported by Marco Polo as early as 1271, although the Romans already knew about and even the Bible[1] refers to this aggregate of such a wonderful color. Another famous locality where lapis lazuli is mined is in the Andes mountain range of Chile.
Lapis lazuli is often mimicked by a dyed jasper, but it does not show the white and golden patches. Sodalite, one of the components of lapis lazuli, is often mistaken for it, but the color is much paler. There is also a sintered synthetic spinel which imitates lapis lazuli.
Dyeing and impregnation occurs on lesser quality gems and these can be easily removed by acetone. Leaving these stones in the sun for a too long a period of time will cause the dye or impregnation to stain the environment.
| Gemological information for lapis lazuli | |
|---|---|
| Color | Cobalt blue with white or golden patches (calcite and pyrite) |
| Crystal structure | Rock |
| Refractive index | ~1.50 |
| Durability | Durable |
| Hardness | 5.5 |
| Treatments | Dying, imitations |
| Country of origin | Afghanistan, Chile, Russia |
Notes
Sources consulted
- Gemmology Third Edition - Peter G. Read
- Gems, Their Sources, Descriptions and Identification 4th edition - Robert Webster, B.W. Anderson
Online G&G articles on lapis lazuli
- Spring 1936, The specific gravity of lapis lazuli, p. 8, 1p.
- Summer 1941, Colorado Lapis Lazuli, p. 154, 3pp.
- Fall 1954, A New Substitute for Lapis Lazuli, by Anderson, p. 88, 2pp.
- Summer 1962, A lapis lazuli test, p. 315, 1p.
- Spring 1963, Translucent lapis lazuli (showing absorption spectrum), p. 20, 1p.
- Summer 1963, Testing stained lapis lazuli, p. 44, 1p.
- Fall 1965, Notes on lapis lazuli and its treatment, p. 337, 2pp.
- Summer 1967, Dyed lapis lazuli, p. 180, 2pp.
- Spring 1968, Dyed waxed lapis lazuli, p. 278, 1p.
- Summer 1970, A beautiful Pietre Dure (Italian inlay) lapis lazuli, p. 188, 1p.
- Fall 1974, Imitation lapis lazuli, p. 327, 4pp.
- Fall 1976, Non-Single-Crystal Synthetics (synthetic Gilson lapis lazuli), by Nassau, p. 194, 5pp.