<span>Extrusive Igneous Rocks. Extrusive igneous rocks form when magma reaches the Earth's surface a volcano and cools quickly. Most extrusive (volcanic) rocks have small crystals. Examples include basalt,rhyolite, andesite, and obsidian.</span>
Answer: The correct answer is : This type of rock is formed by means of the hot magma that flows (extrudes) from the interior of the earth towards the surface in the form of lava or explodes in the atmosphere. Magma cools more quickly in the open air or under the waters of the sea and in a short time the crystals grow. Some examples of extrusive rocks are: pumice, obsidian, andresite, rhyolite, basalt, scomia, fledspar and gabbro.
