Gemmology
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Thursday, 1 October 2020


Gemmology — gemstones — characteristics, classification, specimens, library
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GEMMOLOGY — GEMSTONES

characteristics, classification, specimens, library

As gemstones we accept cut specimens of crystals of natural mineral species having a visible transparency and certain durability. From over 4800 known minerals (according to data of the International Mineralogical Association), approximately 150 satisfy the above conditions and form crystals of sufficient size to be cut.

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

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Classification
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Cerussite

— Common in the oxidised zone of lead deposits, where it may constitute an important ore (Anthony et al., 2001—2005). Faceted specimens are very rare. The largest faceted stone is a 408 carat from Tsumeb, Namibia (Arem, 1987: 64).
Cerussite

The section ‘Repository’ contains data and photos of 760 specimens of gemstones. The smallest is just 1.96 mm (0.02 ct) ruby from Mozambique, and the largest — 70.11 mm (326.60 ct) rock crystal from Africa. Besides there are 8 specimens of synthetic stones.

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Repository
Amethyst — specimen 0675

Some exceptional specimens of gemstones from our ‘Repository’

More specimens of gemstones
Indicolite — specimen 0330
Amethyst — specimen 0336
Indicolite — specimen 0338
Peridot — specimen 0340

— More from ‘Repository

Currently there are 283 bibliographical references and abstracts to publications with gemmological or mineralogical thematics in the ‘Library’. The section comprises also a glossary with 391 terms.
Library
Glossary

decagon — rare shape in faceting a gemstone
demantoid — variety of andradite; see demantoid in ‘Classification’
diabase — a mafic, subvolcanic rock; equivalent to volcanic basalt
diagenesis — the change of sediment or existing sedimentary rocks into sedimentary rock during and after rock formation, at temperatures and pressures less than that required for the formation of metamorphic rocks
Publications

Bruun-Neergard, T. C., 1807 — De la haüyne, nouvelle substance minérale — Published in 1807 in ‘Journal des Mines’; contains the original description of the mineral haüyne.
Bruhns, W., Busz, K., 1890 — Phosphosiderit, ein neues Mineral von der Grube Kalterborn bei Eiserfeld im Siegenschen — Published in 1890 in ‘Zeitschrift für Krystallographie und Mineralogie’; contains the original description of the mineral phosphosiderite.