Diabase is used in the construction industry as trap rock or dimension stone. When the diabase contains colorful labradorite crystals, it makes an especially nice architectural stone. Gabbro is a coarse-grained, dark-colored, intrusive igneous rock that contains feldspar, pyroxene, and sometimes olivine. The specimen shown above is about two inches five centimeters across. Diorite is a coarse-grained, intrusive igneous rock that contains a mixture of feldspar , pyroxene, hornblende , and sometimes quartz.
Obsidian is a dark-colored volcanic glass that forms from the very rapid cooling of molten rock material. It cools so rapidly that crystals do not form. Granite is a coarse-grained, light-colored, intrusive igneous rock that contains mainly quartz , feldspar, and mica minerals. The specimen above is about two inches five centimeters across.
Peridotite is a coarse-grained intrusive igneous rock that is composed almost entirely of olivine. It may contain small amounts of amphibole, feldspar, quartz , or pyroxene. Pegmatite is a light-colored, extremely coarse-grained intrusive igneous rock. It forms near the margins of a magma chamber during the final phases of magma chamber crystallization.
It often contains rare minerals that are not found in other parts of the magma chamber. Rhyolite is a light-colored, fine-grained, extrusive igneous rock that typically contains quartz and feldspar minerals. Pumice is a light-colored vesicular igneous rock. It forms through very rapid solidification of a melt. Igneous rocks may or may not be found naturally where you live, but chances are that you have seen materials made from igneous rocks.
One of the most common igneous rocks is granite Figure 4. Granite is used extensively in building materials and making statues. Perhaps you have used a pumice stone to smooth your skin or to do jobs around the house. Pumice is another example of an igneous rock Figure 4. Pumice is used to make stone-washed denim jeans! You also probably use igneous rock when you brush your teeth every morning.
Ground up pumice stone is sometimes added to toothpaste to act as an abrasive material that scrubs your teeth clean. Igneous rocks form when molten material cools and hardens. They make up most of the rocks on Earth. Most igneous rock is buried below the surface and covered with sedimentary rock, and so we do not often see just how much igneous rock there is on Earth. Figure 4. Twitter Facebook Pinterest Google Classroom.
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Related Resources. View Collection. View Article. Metamorphic Rocks. The Rock Cycle. Generally, the mineral constituents of fine-grained extrusive igneous rocks can only be determined by examination with a microscope, so only an approximate classification can usually be made in the field. Hypabyssal rock is a form of intrusive igneous rock that solidifies at medium to shallow depths within the crust, usually in fissures as dikes and intrusive sills.
These rocks typically have an intermediate grain size and texture between that of intrusive and extrusive rock. As might be expected, they show structures that intermediate between those of extrusive and plutonic rocks.
Common examples of subvolcanic rocks are diabase, quartz-dolerite, micro-granite and diorite. Igneous rocks are classified according to their mode of occurrence, texture, mineralogy, chemical composition, and the geometry of the igneous body. Two important variables that are used for the classification of igneous rocks are particle size and the mineral composition of the rock. Feldspar, quartz, olivines, micas, etc. Types of igneous rocks with other essential minerals are very rare.
In simplified classification, igneous rocks are separated by the type of feldspar present, the presence or absence of quartz, and — in cases where feldspar or quartz are not present — by the type of iron or magnesium minerals present.
Rocks containing quartz are silica-oversaturated, while rocks with feldspathoids are silica-undersaturated. Igneous rocks which have crystals large enough to be seen with the unaided eye are classified as phaneritic, while those with crystals too small to be seen are aphanitic.
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