Mica is used to make optical elements in electronics. The mineral pollucite is the main source of the metal cesium. Examples of intrusive igneous rocks are diorite , gabbro , granite , pegmatite , and peridotite . Walk through the minerals in the pegmatite with students. Porphyritic – Some crystals can be seen, and some crystals cannot be seen. What type of igneous rock is pegmatite (intrusive or extrusive)? Sometimes, the large crystals that form within the rock are valuable gemstones. Pegmatitic – Minerals grow extremely large. Which rock is very light gray? Igneous rocks form when magma (molten rock) cools and crystallizes, either at volcanoes on the surface of the Earth or while the melted rock is still inside the crust. The most common minerals in pegmatite are feldspar, mica, and quartz. Extrusive rock, any rock derived from magma (molten silicate material) that was poured out or ejected at Earth’s surface. Pumice. Depending on their silica content, they are called (in ascending order of silica content) gabbro, diorite, granite and pegmatite. More violent volcanic eruptions cause the fragmentation. Intrusive igneous rocks crystallize below Earth's surface, and the slow cooling that occurs there allows large crystals to form. Examples of intrusive igneous rocks are diorite, gabbro, granite, pegmatite, and peridotite. Granite pegmatite typically contains feldspar, mica, and quartz. Pegmatite is a form of igneous rock consisting of extremely coarse granite resulting from the crystallization of magma rich in rare elements. Intrusions vary widely, from mountain-range-sized batholiths to thin veinlike fracture fillings of aplite or pegmatite. REMEMBER ... Use information about texture, grain size, intrusive or extrusive, vesicular or non-vesicular to narrow your choices to certain igneous rocks that fit the There are five types of intrusive rocks, which are granite, pegmatite, gabbro, diorite and peridotite. The melt contains water and often volatile carbon dioxide and fluorine. Pegmatite is an economically-important rock because it is the source material for lithium, cesium, and rare earth elements and because it may hold large gemstones. A dike is such a formation that cuts across the layering of the rocks it intrudes. PEGMATITE - cooled at depth inside the magma chamber - large crystals. Pegmatite is called an intrusive igneous rock because it forms when magma solidifies under the Earth's surface. For example, gabbro, granite and pegmatite are intrusive rocks. It is important to note that the main difference between them is . Extrusive rocks crystallize at the surface and have fine-grained to glassy textures. All Rights Reserved. Intrusive Igneous Rocks. Pegmatite texture occurs during magma cooling when some minerals may grow so large that they become massive (the size ranges from a few centimeters to several meters). The rock tends to be associated with granite. In other cases, lava explodes violently from a volcano, expelling it into the open atmosphere where it solidifies almost instantly. Pegmatites form from waters that separate from a magma in the late stages of crystallization; this activity often occurs in small pockets along the margins of a batholith. So crystals grow very large for intrusive igneous rocks. Notice the large grains of pink, white, and gray minerals. There is no defined mineralogy for pegmatite; any plutonic rock may form pegmatite. While most pegmatite does consist of granite, the rock is defined by its structure, not its composition, and. Igneous rocks are divided into two types -- volcanic rock (extrusive) and plutonic rock (intrusive) -- depending on where the magma cools. Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. For example, "lithian pegmatite" contains lithium, while "boron pegmatite" contains boron or yields tourmaline. basalt - intrusive or extrusive? How the igneous rocks occurred can be attributed to where in the earth, what surroundings and conditions created them. Aphanitic – Crystals are too small to see. For instance, a rock called pegmatite is formed by the crystallization of magma enriched with water in the veins of other rocks, and may contain beryl, tourmaline and topaz. Red corundum (ruby) in zoisite may be found in metamorphic rock and in pegmatite. However, pegmatite is enriched with trace elements, which make it even more interesting and commercially important. In contrast, when magma solidifies outside the Earth's surface, it forms an extrusive igneous rock. The magma cools very slowly to allow larger crystals. 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