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Trachyandesite is an extrusive igneous rock with a composition between trachyte and andesite. It has little or no free quartz, but is dominated by sodic plagioclase and alkali feldspar. It is formed from the cooling of lava enriched in alkali metals and with an intermediate content of silica. [1] [2]
Trachyte (/ ˈ t r eɪ k aɪ t, ˈ t r æ k-/) is an extrusive igneous rock composed mostly of alkali feldspar. It is usually light-colored and aphanitic (fine-grained), with minor amounts of mafic minerals, [ 1 ] and is formed by the rapid cooling of lava (or shallow intrusions) enriched with silica and alkali metals .
Edziza trachyte is mineralogically similar to trachyte of the Kakiddi Formation which was erupted 0.3 million years ago during the final stages of the fourth magmatic cycle. However, the Kakiddi trachyte flows travelled along gently sloping valleys for at least 10 kilometres (6.2 miles), suggesting that they were extruded more fluidly than ...
Orthoclase phenocrysts within a finer-grained matrix of a granite porphyry. The matrix or groundmass of a rock is the finer-grained mass of material in which larger grains, crystals, or clasts are embedded. The matrix of an igneous rock consists of finer-grained, often microscopic, crystals in which larger crystals, called phenocrysts, are ...
The composition of rhomb porphyry places it in the trachyte–latite classification of the QAPF diagram. [12] Rhomb porphyry is found in continental rift areas, including the East African Rift (including Mount Kilimanjaro), [13] Mount Erebus near the Ross Sea in Antarctica, [14] the Oslo graben in Norway, [12] and south-central British Columbia ...
Thin sections are prepared in order to investigate the optical properties of the minerals in the rock. This work is a part of petrology and helps to reveal the origin and evolution of the parent rock. A photograph of a rock in thin section is often referred to as a photomicrograph.
Phonolite is a variation of the igneous rock trachyte that contains nepheline or leucite rather than quartz. [1] It has an unusually high (12% or more) Na 2 O + K 2 O content, defining its position in the TAS classification of igneous rocks. Its coarse grained (phaneritic) intrusive equivalent is nepheline syenite. Phonolite is typically fine ...
Trachybasalt is a volcanic rock with a composition between trachyte and basalt. It resembles basalt but has a high content of alkali metal oxides . Minerals in trachybasalt include alkali feldspar , calcic plagioclase , olivine , clinopyroxene and likely very small amounts of leucite or analcime .