GENERAL GEOLOGY

Detailed explanation-1: -Extrusive, or volcanic, igneous rock is produced when magma exits and cools above (or very near) the Earth’s surface. These are the rocks that form at erupting volcanoes and oozing fissures.

Detailed explanation-2: -Extrusive (Volcanic) Rocks Extrusive igneous rocks are also termed volcanic rocks-named for Vulcan, the Roman god of fire. Volcanic rocks have generally smaller crystal size and usually have a very-fine-grained or glassy groundmass that formed due to rapid cooling at the time of eruption.

Detailed explanation-3: -Intrusive or extrusive. Intrusive (plutonic) rocks form when magma solidifies within the crust below the surface. It usually cools slowly and produces large crystals. Extrusive (volcanic) rocks form when magma erupts onto the surface of the Earth as lava flows, and usually cools quickly producing small crystals.

Detailed explanation-4: -Lava flow in Hawaii Lava cools quickly on the surface of the earth and forms tiny microscopic crystals. These are known as fine-grained extrusive, or volcanic, igneous rocks. Extrusive rocks are often vesicular, filled with holes from escaping gas bubbles.

Detailed explanation-5: -There are several types of extrusive rock including basalt, andesite, and rhyolite. Obsidian is another example of extrusive rock and is a type of volcanic glass that cools so quickly that no crystals form. Pumice is another example of extrusive rock with lots of vesicles.