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| Zwaan, J.C.. |
| The Dr H.M.E. Schürmann collection is stored at the National Museum of Natural History in Leiden, The Netherlands. It mainly consists of Precambrian rocks, but also includes other crystalline rocks and minerals, which were collected from all over the world. In order to provide a quick reference to localities of interest, an overview of the most important geographical locations is given. During his life and particularly after his retirement, Schürmann spent much of his time studying the Precambrian in North Africa. As a result, he gathered an extensive and well-documented collection of Precambrian rocks and minerals from Egypt and an irreplaceable collection of Precambrian rocks from drill-cores of deep wells situated in Libya. Both collections are... |
| Tipo: Article / Letter to the editor |
Palavras-chave: 38.29. |
| Ano: 1994 |
URL: http://www.repository.naturalis.nl/record/317408 |
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| Zwaan, J.C.. |
| As one of the most valuable gemstones, emeralds are known to occur in several countries of the world, such as Colombia, Zambia, Brazil, Pakistan, Afghanistan, Russia, Madagascar and Zimbabwe. The emerald deposits at Sandawana, Zimbabwe, are described, the emeralds from this deposit characterised and a model of emerald formation presented; this is compared with existing models. The emeralds from Sandawana, Zimbabwe, show relatively constant physical properties, with high refractive indices and specific gravities. They are characterized by laths and fibres of amphibole, both actinolite and cummingtonite. Other common inclusions are albite and apatite. Rare, opaque and chromium-rich inclusions constitute a new variety of ilmenorutile. Compared to emeralds... |
| Tipo: Article / Letter to the editor |
Palavras-chave: Emerald; Sandawana; Zimbabwe; Gemmology; Petrology; Geothermometry; Geochronology; 38.30. |
| Ano: 2006 |
URL: http://www.repository.naturalis.nl/record/209632 |
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