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  2. Phenocryst - Wikipedia

    en.wikipedia.org/wiki/Phenocryst

    Some rocks contain both microphenocrysts and megaphenocrysts. [2] In metamorphic rocks, crystals similar to phenocrysts are called porphyroblasts. Phenocrysts are more often found in the lighter (higher silica) igneous rocks such as felsites and andesites, although they occur throughout the igneous spectrum including in the ultramafics.

  3. Porphyritic - Wikipedia

    en.wikipedia.org/wiki/Porphyritic

    The large grain in the middle is of a much different size class than the small needle-like crystals around it. Scale box in millimeters. 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.

  4. Crystal - Wikipedia

    en.wikipedia.org/wiki/Crystal

    Crystals found in rocks typically range in size from a fraction of a millimetre to several centimetres across, although exceptionally large crystals are occasionally found. As of 1999 [update] , the world's largest known naturally occurring crystal is a crystal of beryl from Malakialina, Madagascar , 18 m (59 ft) long and 3.5 m (11 ft) in ...

  5. 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.

  6. Pegmatite - Wikipedia

    en.wikipedia.org/wiki/Pegmatite

    Large crystals are favored. In normal igneous rocks, coarse texture is a result of slow cooling deep underground. [14] It is not clear if pegmatite forms by slow or rapid cooling. [15] In some studies, crystals in pegmatitic conditions have been recorded to grow at a rate ranging from 1 m to 10 m per day. [16]

  7. Igneous textures - Wikipedia

    en.wikipedia.org/wiki/Igneous_textures

    Phaneritic (phaner = visible) textures are typical of intrusive igneous rocks, these rocks crystallized slowly below Earth's surface. As magma cools slowly the minerals have time to grow and form large crystals. The minerals in a phaneritic igneous rock are sufficiently large to see each individual crystal with the naked eye.

  8. Matrix (geology) - Wikipedia

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

    The matrix of an igneous rock consists of finer-grained, often microscopic, crystals in which larger crystals, called phenocrysts, are embedded. This porphyritic texture is indicative of multi-stage cooling of magma. For example, porphyritic andesite will have large phenocrysts of plagioclase in a fine-grained matrix.

  9. Portal:Minerals - Wikipedia

    en.wikipedia.org/wiki/Portal:Minerals

    The crystal structure of pyrite is primitive cubic, and this is reflected in the cubic symmetry of its natural crystal facets. In crystallography, the cubic (or isometric) crystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals.

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