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The individual crystals in an aphanitic igneous rock are not distinguishable to the naked eye. Examples of aphanitic igneous rock include basalt, andesite, and rhyolite. Glassy or vitreous textures occur during some volcanic eruptions when the lava is quenched so rapidly that crystallization cannot occur. The result is a natural amorphous glass ...
Llanite is a porphyritic rhyolite with distinctive phenocrysts of blue quartz (a rare quartz color) and perthitic feldspar (light grayish-orangeish). The brown, fine-grained groundmass consists of very small quartz, feldspar, and biotite mica crystals.
Typical acidic rocks are granite or rhyolite. The term is used in chemical classification of igneous rock based on the content of silica (SiO 2 ). Due to the fact that chemical analyzes are not always available, especially during the fieldwork, classification based on the mineral (modal) composition is more often used (dividing the igneous ...
Llanite – Type of mineral – A hypabyssal rhyolite with microcline and blue quartz phenocrysts from the Llano Uplift in Texas; Luxullianite – Rare type of granite; Mangerite – Plutonic intrusive igneous rock, that is essentially a hypersthene-bearing monzonite; Minette – A variety of lamprophyre
The word granite goes back at least to the 1640s and is derived either from French granit or Italian granito, meaning simply "granulate rock". [28] The term rhyolite was introduced in 1860 by the German traveler and geologist Ferdinand von Richthofen [ 29 ] [ 30 ] [ 31 ] The naming of new rock types accelerated in the 19th century and peaked in ...
Rhyolite was mined there starting 11,500 years ago. [32] Tons of rhyolite were traded across the Delmarva Peninsula, [32] because the rhyolite kept a sharp point when knapped and was used to make spear points and arrowheads. [33] Obsidian is usually of rhyolitic composition, and it has been used for tools since prehistoric times. [34]
"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.
A block of granite in 2017 from the Fletcher Granite Company. The granite is described as a light gray or light pinkish-gray to a medium, slightly pinkish or pinkish and greenish-gray biotite granite with spots from 0.2 to 0.5 inches (5.1 to 12.7 mm) across and in some cases tapering out to 1 inch (25 mm) in length. [1]
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