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Date submitted2008-10-13
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Date accepted2008-12-02
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Date published2009-12-11
Principles of rational classification of magmatic rocks
- Authors:
- V. V. Dolivo-Dobrovolsky
The classification of igneous rocks approved in Petrographic code is not quite good, as well as the classification offered by the commission of the International Union of geological sciences. The rational and practically convenient classification of igneous rocks must take into account positive aspects of existing systematics. The division of igneous rocks into three classes (plutonic, volcanic and hypabissal) according to criteria stated in Petrographic code is well founded. The further division should be based on mineral contents; chemical composition should be used only if mineral contents can not be determined. Chemical composition must be recalculated to contents of normative minerals for classification purposes.
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Date submitted1948-07-20
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Date accepted1948-09-27
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Date published1949-11-04
Genetic relationship of crystal nests with quartz veins and the origin of cavities
- Authors:
- A. E. Karyakin
In the early stages of studying the piezo-optical quartz deposits of the Northern Urals, some geologists believed that crystal nests had no genetic connection with quartz veins. Geologists came to this conclusion because at that time the bulk of piezo-optical quartz was mined not from crystal nests, but from placers, and geologists did not have enough data to correctly resolve this issue. Later, in connection with the transition to exploration of primary deposits, it was established that in most cases quartz veins and crystal nests are located in the same cracks. The asymmetrical arrangement of crystal nests in relation to quartz veins does not give reason to deny the genetic relationship of both, but only indicates a later formation of crystal nests compared to quartz veins. In all likelihood, after the formation of quartz veins, there was a fairly long intermineralization break, after which crack formation and the flow of hydrothermal solutions resumed. The duration of the intermineralization break can be judged by the sharp change in the nature of the hydrothermal solutions - from highly supersaturated with silicic acid (during the formation of quartz veins) to normal (during the formation of quartz crystals). Consequently, quartz veins and crystal nests are derivatives of a single magmatic chamber, but they were only formed in different phases of a single hydrothermal process.