Basalt is generally found in volcanoes that lie in the ocean. For example, Kilauea in Hawaii is a perfect example for a volcano made up of basalt. Obsidian rock forms extrusively and cools quickly. Obsidian is a natural glass originally molten magma rich in silica. It lacks the minerals which give it the smooth texture.
Granite is a type of rock that forms intrusively and slowly.
It usually is found in numerous volcanoes that inhabit on land. Another important type of volcanic rock is pumice. Pumice forms from the violent separation of gas from lava to produce light colored frothy rock fragments. Three Cinder cones are the simplest types of volcanoes in the shape of a circular or oval cone. With the naked eye, a cinder cone resembles a large hill or mound.