Hallflinta
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Hallflinta is the name for fine-grained, often striped or banded, moderately metamorphic acidic ( rhyolite ) volcanics or pyroclasts (metavulcanites, metapyclasts). They have a dense structure. The name comes from Swedish and the translation Felsenflint indicates that there are sharp splinters in the case of breakage, as with Flint . The name is regionally limited mainly to Scandinavia. The rocks are typically gray or reddish and consist of fine crystalline quartz and feldspar, more rarely also with finely flaked light mica, with millimeter-sized feldspar inserts from the original volcanic or flames (lenticular flow structures in pyroclasts). Metamorphic new mineral formations are often finely flaked sheet silicates .
They can mainly be assigned to the green schist facies , but a clear assignment to a metamorphic facies is not possible, as is the case with leptites.
Leptites , a light-colored granulite made from feldspar and quartz (finer-grained than gneiss ) , have a similar origin but are more coarse-grained . They are sometimes foiled and light, gray, yellowish-gray or reddish in color. The name also comes from Sweden and is regionally limited to Scandinavia. They can often be easily mistaken for fine-grained igneous rocks (if there is no foil and without knowledge of the embedding conditions), but they come from acidic volcanic rocks.
In 2005 the IUGS subcommittee on systematics of metamorphic rocks did not include the designations Hälleflinta and Leptit among the recommended designations.
literature
- Roland Vinx: Rock determination in the field . 4th edition. Springer Spectrum, 2015, ISBN 978-3-642-55417-9 , p. 386 f.
- Hallflinta . In: Encyclopædia Britannica . 11th edition. tape 12 : Gichtel - harmonium . London 1910, p. 855 (English, full text [ Wikisource ]).
Web links
- Matthias Bräunlich Kristallin.de
Individual evidence
- ↑ According to Encyclopedia Britannica 1911 also greenish and in other colors
- ↑ Roland Vinx: Rock determination in the terrain , p. 386
- ↑ Roland Vinx: Rock determination in the terrain , p. 386. According to Vinx, the IUGS recommended equating it with Hornfels in 2005 , but this was again omitted in 2007 because Hälleflinta and Leptite are not contact-metamorphic.