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The result is a natural amorphous glass with few or no crystals. Examples include obsidian. Pegmatitic texture occurs during magma cooling when some minerals may grow so large that they become massive (the size ranges from a few centimetres to several metres). This is typical of pegmatites.
"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.
glassybaby is a company based in Seattle, Washington that produces handmade glass votive candle holders, called glassybaby, which are sold online and at stores in the Seattle area and Oregon. The company plans to open a store in Montana as of 2023 [update] .
Rhyolites that cool too quickly to grow crystals form a natural glass or vitrophyre, also called obsidian. [13] Slower cooling forms microscopic crystals in the lava and results in textures such as flow foliations, spherulitic, nodular, and lithophysal structures. Some rhyolite is highly vesicular pumice. [5]
In extrusive rocks, the phenocrysts are surrounded by a fine-grained (aphanitic) matrix or groundmass of volcanic glass or non-visible crystals, commonly seen in porphyritic basalt. Porphyritic intrusive rocks have a matrix with individual crystals easily distinguished with the eye, but one group of crystals appearing clearly much bigger than ...
This is an accepted version of this page This is the latest accepted revision, reviewed on 3 January 2025. Classified advertisements website Craigslist Inc. Logo used since 1995 Screenshot of the main page on January 26, 2008 Type of business Private Type of site Classifieds, forums Available in English, French, German, Dutch, Spanish, Italian, Portuguese Founded 1995 ; 30 years ago (1995 ...
Quartz-porphyry, in layman's terms, is a type of volcanic rock containing large porphyritic crystals of quartz. [ 1 ] [ 2 ] These rocks are classified as hemi-crystalline acid rocks . Structure
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 ...