Lava is what kind of rock

Typically, eruption occurs when there is an increase in temperature, a decrease in pressure or a change in composition. There are over types of igneous rocks, all of which have diverse properties; however, they can all be classified into three categories. Extrusive, also known as volcanic, rocks are a type of igneous rock that form at the crust's surface as a result of volcanic activity. This type of rock occurs when lava flows on or above the Earth's surface and cools down rapidly. The lava comes from the upper mantle layer, 30 to 90 miles beneath the surface, and cools within a few weeks.

Because the magma cools and solidifies quickly, the crystals that form do not have time to grow very large, and therefore most extrusive rocks are finely grained. The most common type of extrusive rock is basalt.

Intrusive, or plutonic, igneous rocks form underneath the Earth's surface when magma flows into underground chambers or tunnels. The rock is not exposed to the atmosphere above surface, so the magma cools slowly which allows large mineral crystals to form within the rock. It takes thousands of years for Intrusive rocks to form. Hypabassal, or subvolcanic, rock derives from magma that has solidified at a shallow depth of the volcano, mainly in dykes and sills.

This type of rock is formed in between extrusive and intrusive rock, and similarly has a texture in between that of intrusive and extrusive rock. The Auckland volcanic field has erupted this type of hot, runny iron-rich lava, and the landscape is dotted with mountains made from basalt and scoria a red-coloured rock that contains large amounts of iron-rich minerals.

Both rock types are excavated for building materials and landscaping. Some scoria rocks fall within the andesite classification because of their chemical composition.

Some rhyolitic rocks are quite light, for example, pumice, which may still have evidence of the bubbles of gas trapped as the rock solidified. 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.

Pumice is ground up and used today in soaps, abrasive cleansers, and also in polishes. Rhyolite is very closely related to granite. The difference is rhyolite has much finer crystals. These crystals are so small that they can not be seen by the naked eye.

Rhyolite is an extrusive igneous rock having cooled much more rapidly than granite giving it a glassy appearance. The minerals that make up rhyolite are quartz, feldspar, mica, and hornblende. Gabbros are dark-colored, coarse-grained intrusive igneous rocks. They are very similar to basalts in their mineral composition. They are composed mostly of the mineral plagioclase feldspar with smaller amounts of pyroxene and olivine. Obsidian is a very shiny natural volcanic glass.

When obsidian breaks it fractures with a distinct conchoidal fracture. Notice in the photo to the left how it fractures. Obsidian is produced when lava cools very quickly. The lava cools so quickly that no crystals can form. When people make glass they melt silica rocks like sand and quartz then cool it rapidly by placing it in water.

Obsidian is produced in nature in a similar way. Obsidian is usually black or a very dark green, but it can also be found in an almost clear form. Ancient people throughout the world have used obsidian for arrowheads, knives, spearheads, and cutting tools of all kinds. Today obsidian is used as a scalpel by doctors in very sensitive eye operations. Write the answers to the following questions in complete sentences on a piece of paper. In your own words write a definition for magma and lava.

What is the difference between intrusive and extrusive igneous rocks? What are the most common extrusive and intrusive igneous rocks? What is the difference between granite and rhyolite and how are they similar? Skip to main content. Toggle menu Go to search page. Search Field. Igneous Rocks Lesson