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  2. Rhyolite - Wikipedia

    en.wikipedia.org/wiki/Rhyolite

    An extrusive igneous rock is classified as rhyolite when quartz constitutes 20% to 60% by volume of its total content of quartz, alkali feldspar, and plagioclase and alkali feldspar makes up 35% to 90% of its total feldspar content. Feldspathoids are not present. This makes rhyolite the extrusive equivalent of granite.

  3. Porphyry (geology) - Wikipedia

    en.wikipedia.org/wiki/Porphyry_(geology)

    "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.

  4. Igneous textures - Wikipedia

    en.wikipedia.org/wiki/Igneous_textures

    Igneous textures include the rock textures occurring in igneous rocks. Igneous textures are used by geologists in determining the mode of origin of igneous rocks and are used in rock classification. The six main types of textures are phaneritic, aphanitic, porphyritic, glassy, pyroclastic, and pegmatitic.

  5. Andesite - Wikipedia

    en.wikipedia.org/wiki/Andesite

    Andesite (/ ˈ æ n d ə z aɪ t /) [1] is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained to porphyritic in texture, and is composed predominantly of sodium-rich plagioclase plus pyroxene or hornblende. [2]

  6. Igneous rock - Wikipedia

    en.wikipedia.org/wiki/Igneous_rock

    Grain size in igneous rocks results from cooling time so porphyritic rocks are created when the magma has two distinct phases of cooling. [18] Igneous rocks are classified on the basis of texture and composition. Texture refers to the size, shape, and arrangement of the mineral grains or crystals of which the rock is composed. [citation needed]

  7. Llanite - Wikipedia

    en.wikipedia.org/wiki/Llanite

    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.

  8. List of rock types - Wikipedia

    en.wikipedia.org/wiki/List_of_rock_types

    Porphyry – Textural form of igneous rock with large grained crystals in a fine matrix; Pumice – Extremely vesicular volcanic rock, typically light-colored; Pyroxenite – Igneous rock - a coarse grained plutonic rock composed of >90% pyroxene; Quartz diorite – Igneous, plutonic rock – A diorite with >5% modal quartz

  9. Porphyritic - Wikipedia

    en.wikipedia.org/wiki/Porphyritic

    Porphyritic is an adjective used in geology to describe igneous rocks with a distinct difference in the size of mineral crystals, with the larger crystals known as phenocrysts. Both extrusive and intrusive rocks can be porphyritic, meaning all types of igneous rocks can display some degree of porphyritic texture.

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