Iets over gangen, porfieren en glazen
Grondboor & Hamer , Volume 46 - Issue 3 p. 65- 70
After a short introduction on the egyptian rock, first named porphyry (an andesite) and its colour, an overview is given of the origin and properties of rhyolitic rocks. It briefly touches on the following topics: origin of porphyritic texture, viscosity and explosivity of rhyolitic magmas, types of rhyolite bodies, ignimbrites and their lithologic characteristics, phenocryst minerals and the order of crystallization in granitic magmas, possible causes of magmatic corrosion of henocrysts, and, lastly, on growth of megacrysts of potash feldspar, quarz and biotite in granitic and tonalitic rocks and their enclaves. Some new data are presented, among other things on the subject of megacrysts. All examples of rocks mentioned in this paper are taken from the collections of the former Geology Department at Groningen University.
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