When does igneous rock form

As hot, molten rock rises to the surface, it undergoes changes in temperature and pressure that cause it to cool, solidify, and crystallize.

However, some are also formed on the surface as a result of volcanic activity. Those that fit into the former category are known as intrusive or plutonic rocks, while those that fit into the latter are known as extrusive or volcanic rock. In addition to these, there is also hypabyssal or subvolcanic rock , a less common form of igneous rock that is formed within the Earth between plutonic and volcanic rocks. As this rock is surrounded by pre-existing rock, the magma cools slowly, which results in it being coarse grained — i.

The most common types of plutonic igneous rock are granite, gabbro, or diorite. The central cores of major mountain ranges consist of large bodies of intrusive igneous rocks — also known as batholiths — since they are the result of magma cooling within preexisting solid rock on the surface.

In addition to batholiths, other types of igneous rock structures include stocks, laccoliths, lopoliths, phacolith, chonliths, sills, dikes, and volcanic pipes or necks.

All of these are to be found in subterranean layers, but can sometimes breach the surface due to tectonic activity. Extrusive rocks are so named because they are the result of magma pouring onto the surface of the planet and cooling. When it reaches the surface, either on a continental shelf as a volcano or on the ocean floor as a submarine volcano, it becomes lava, by definition. The viscosity of lava depends upon the temperature composition and crystal content of the molten rock itself.

You never know which particular kernel is going to pop, but you know if you wait long enough, most of them will have popped. All else being equal i. As the number of kernels dwindles, the number of popped corn kernels increases. You could plot the number of kernels left to be popped and the number that have already popped :.

The time scale is determined by the half-life or the time it takes for half the kernels to pop. From looking at the graph, it is obvious that the number remaining at any time decreases with time, and more pop per unit time than pop later, when there are fewer left to pop.

In fact, the number that pop during any interval depends on the number of unpopped kernels that were there at the beginning of the interval. The special number is called "e" and is about 2. The time constant is some number that depends on the rate at which the pop corn pops. I used the number the natural log of 2 0. You can actually plot the curve shown above with a hand calculator.

Radioactivity behaves somewhat like popcorn as describe above. There are unstable isotopes of certain elements. Key Terms Felsic : Derived from the words feldspar and silica to describe an igneous rock having abundant light-colored minerals such as quartz, feldspars, or muscovite.

NPS photo by Janice Wei. Extrusive Igneous Rock Extrusive, or volcanic, igneous rock is produced when magma exits and cools as lava at or near the Earth's surface. Dark colored diabase dikes intrude through light colored granite at Acadia National Park, Maine. NPS photo by Georgia Hybels. Intrusive Igneous Rock Intrusive, or plutonic, igneous rock forms when magma remains inside the Earth's crust where it cools and solidifies in chambers within pre-existing rock. Featured Video—Yosemite Granite.

Yosemite Nature Notes Granite Many national parks were founded for their geology, and Yosemite is known throughout the world for its exceptional high cliffs and rounded domes. Duration: 7 minutes, 11 seconds. Igneous Rock Textures. Felsic rhyolite with an aphanitic texture. Photo courtesy of Tina Kuhn.

If molten salol cools slowly, you get big crystals. If it cools quickly, you get small crystals. Igneous rocks Igneous rocks are formed from molten rock that has cooled and solidified.

What are igneous rocks like? The size of the crystals depends on how quickly the molten magma solidified: magma that cools slowly will form an igneous rock with large crystals lava that cools quickly will form an igneous rock with small crystals This means that we get two main types of igneous rock, extrusive and intrusive, as shown in the table: Extrusive Intrusive Where the magma cooled On the surface Underground How fast the magma cooled Quickly Slowly Size of crystals Small Large Examples Obsidian and basalt Granite and gabbro Extrusive igneous rocks form from magma that erupted onto the surface as lava , where it cooled quickly.