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Rose muscovite from the Harding pegmatite mine Blue apatite crystals at the Harding pegmatite mine. Pegmatites form under conditions in which the rate of new crystal nucleation is much slower than the rate of crystal growth. Large crystals are favored. In normal igneous rocks, coarse texture is a result of slow cooling deep underground. [14]
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.
Colors include shades of raspberry red to orange-red and pink.Recovered from miarolitic cavities in the granitic pegmatite fields of Fianarantsoa province, southern Madagascar, the pezzottaite crystals were small—no more than about 7 cm (2.8 in) in their widest dimension—and tabular or equant in habit, and few in number, most being heavily included with growth tubes and liquid feathers.
The central portions of pegmatites are often miarolitic as the pegmatite dike crystallizes from the outside walls toward the center. The volatile portion of the magma is gradually excluded from the forming crystal phases until it becomes trapped within the body and forms the cavities which often contain minerals of elements incompatible with ...
It occurs in lithium-bearing pegmatites with spodumene, lepidolite, and tourmaline. Petalite is an important ore of lithium, and is converted to spodumene and quartz by heating to ~500 °C and under 3 kbar of pressure in the presence of a dense hydrous alkali borosilicate fluid with a minor carbonate component. [ 8 ]
The high water content of the magma made it possible for the crystals to grow quickly, so pegmatite crystals are often quite large, which increases the likelihood of gem specimens forming. Chrysoberyl can also grow in the country rocks near to pegmatites, when Be- and Al-rich fluids from the pegmatite react with surrounding minerals.
Rosacea. What it looks like: Rosacea causes redness and thick skin on the face, usually clustered in the center.Easy flushing, a stinging sensation, and small, pus-filled pimples are other common ...
Aphanite – Igneous rock composed of very small crystals invisible to the naked eye; Borolanite – Variety of nepheline syenite from Loch Borralan, Scotland – A variety of nepheline syenite from Loch Borralan, Scotland; Blue Granite – Variety of monzonite, an igneous rock; Epidosite – Hydrothermally altered epidote- and quartz-bearing rock