Gemmology
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Tuesday, 21 August 2018


Gemmology — gemstones — characteristics, classification, specimens, library
Petschite

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 172 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
Featured

Gadolinite-(Y)

— In granite and alkalic granite pegmatites (Anthony et al., 2001—2005). Faceted specimens are extremely rare.
Gadolinite-(Y)

The section ‘Repository’ contains data and photos of 745 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
Chalcedony — specimen 0685

Some exceptional specimens of gemstones from our ‘Repository’

More specimens of gemstones
Petschite — specimen 0082
Friedelite — specimen 0086
Grossular-hibschite series — specimen 0089
Moonstone — specimen 0095

— 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 392 terms.
Library
Glossary

tapered pentagon — rare shape in faceting a gemstone
tektite — natural glass; see tektite in ‘Classification’
tenebrescence — the ability of minerals to change colour when exposed to sunlight
tetrahedrite — species of mineral; faceted specimens exist
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.