When magma reaches the surface it is then called lava and the eruptions of lava and ash produce volcanoes.
The lava that reaches the Earth's surface will harden and become igneous rock. When the magma does not reach the surface it produces a variety of geologic structures. When lava reaches the surface of the Earth through volcanoes or through great fissures the rocks that are formed from the lava cooling and hardening are called extrusive igneous rocks.
Some of the more common types of extrusive igneous rocks are lava rocks, cinders, pumice, obsidian, and volcanic ash and dust. This is the volcano Paricutin that is located in Mexico. It is erupting cinders and pumice which are examples of extrusive igneous rocks. Millions and even billions of years ago molten rock was cooling and thus hardening into igneous rocks deep under the surface of the Earth.
These rocks are now visible because mountain building has thrust them upward and erosion has removed the softer rocks exposing the much harder igneous rocks. These are called intrusive igneous rocks because the magma has intruded into pre-exiting rock layers. Types of intrusive igneous rocks are granite and basalt. The diagram above shows you a large intrusive igneous body called a batholith. A batholith is the largest of the intrusive bodies.
They are larger than square kilometers and usually form granite cores. As you can see in the diagram above a batholith is a very large intrusive igneous body. There are two types of intrusive bodies that we are going to discuss 1 Discordant and 2 Concordant. A discordant igneous rock body cuts across the pre-exiting rock bed.
Batholiths and dikes are examples of discordant rock bodies. A dike is a vertical or near vertical intrusive igneous rock body that cuts across rock beds. They frequently form from explosive eruptions that crack the area around a volcano with the magma filling the cracks forming a dike.
A concordant igneous rock body runs parallel to the pre-existing bedrock. In the activity, Identifying volcanic rocks students watch a video describing different types of volcanic rocks and then match the chemical composition and type of volcanic eruption each rock is associated with. Making lava fudge is a fun way to help students to learn about the different proportions of minerals in basalt, andesite and rhyolite rocks. In the activity, Lost — a hot rock , students examine an igneous rock and synthesise these observations into a poster that includes characteristic features of igneous rocks.
Add to collection. Nature of science Classification helps scientists organise things into groups. Related content Read about the different types of volcanoes. Activity ideas In the activity, Identifying volcanic rocks students watch a video describing different types of volcanic rocks and then match the chemical composition and type of volcanic eruption each rock is associated with. Go to full glossary Add 0 items to collection. Lava rocks are composed of high amounts of iron and magnesium elements collectively referred to as the ferromagnesian group as well as calcium.
Due to their chemical composition, basalts are the most abundant rock type of the ocean floor and Earth's crust, and are the primary rock layer of the Hawaiian Islands. These rocks contain a relatively low amount of silicon and aluminum elements. The ferromagnesian elements in lava and magma have a rapid cooling rate, resulting in the fine-grain appearance of basalts.
A variety of minerals contribute to the composition of lava rocks. The most common minerals are pyroxine, olivine, amphibole and plagioclase feldspar, although low quantities of hornblende, biotite mica, magnetite and quartz are occasionally present.
Gabbro, a mafic intrusive igneous rock which solidifies beneath the Earth's crust, has the same mineral composition as basalt. At high temperatures, the mafic minerals cool and crystallize very quickly. As a result, some lava rocks have a thin layer of glass particles on their surface. The largest bulldozers and backhoes are regularly humbled by this dense rock, causing contractors to revert to expensive drilling and blasting techniques.
While encountering "blue rock" is a contractor's worst nightmare, it is also the most sought-after rock type by commercial quarry operators. The best grade construction aggregates are from "blue rock. The shade of blue of this rock is closer to gun-metal and is probably caused by the refractive index of the glass.
Eventually, with exposure to the elements, the color of the rock turns to black. As older lava flows weather, the minerals in the rocks oxidize and often turn to clay minerals. The once shiny rock becomes dull and cloudy, or the glassy surface breaks and falls away to expose the dull interior.
One of the most common minerals found in the decomposed rock is hematite, an iron oxide that is usually yellow-brown or rust colored. The abundance of this mineral in the exposed weathered surfaces gives the older flows their distinctive yellow-brown appearance. The color changes of lava from its molten to its solid state are similar to that which you can observe in the tungsten coils of an electric stove.
The higher the temperature of the lava or the stove coils, the brighter the shade of red attained.
0コメント