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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 .
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 ...
In optical mineralogy and petrography, a thin section (or petrographic thin section) is a thin slice of a rock or mineral sample, prepared in a laboratory, for use with a polarizing petrographic microscope, electron microscope and electron microprobe. A thin sliver of rock is cut from the sample with a diamond saw and ground optically flat.
Peperino has been used in Rome and Naples as a building stone, is a trachyte tuff. Pozzolana also is a decomposed tuff, but of basic character, originally obtained near Naples and used as a cement , but this name is now applied to a number of substances not always of identical character.
Sodalite, colorless and transparent in thin section, but frequently pale blue in the hand specimens, is the principal feldspathoid mineral in addition to nepheline. Reddish-brown to black aenigmatite occurs also in these rocks. Extremely iron-rich olivine is rare, but is present in some nepheline syenite.
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 .
Photomicrograph of thin section of latite (in plane polarised light) Photomicrograph of thin section of latite (in cross polarised light) Latite is an igneous, volcanic rock, with aphanitic-aphyric to aphyric-porphyritic texture. It is the volcanic equivalent of monzonite.
"Imperial Porphyry" from the Red Sea Mountains of Egypt A waterworn cobble of porphyry Rhyolite porphyry from Colorado; scale bar in lower left is 1 cm (0.39 in). Porphyry (/ ˈ p ɔːr f ə r i / POR-fə-ree) is any of various granites or igneous rocks with coarse-grained crystals such as feldspar or quartz dispersed in a fine-grained silicate-rich, generally aphanitic matrix or groundmass.