Forming Rocks
When the magma cools it solidifies and forms rocks, the type of rock formed depends on the chemical composition of the magma and how rapidly the magma cools. Magma that reaches the surface to become lava cools rapidly resulting in rocks with small crystals such as basalt. Some of this magma may cool extremely rapidly and will form volcanic glass (rocks without crystals) such as obsidian. Magma that remains trapped below ground in thin intrusions cools slower than magma exposed to the surface and produces rocks with medium sized crystals. Magma that remains trapped in large quantities below ground cools most slowly resulting in rocks with larger crystals - such as granite and gabbro.
Existing rocks that come into contact with magma may be melted and assimilated into the magma. Other rocks adjacent to the magma may be altered by contact metamorphism or metasomatism as they are affected by the heat and escaping or externally circulating hydrothermal fluids.
Read more about this topic: Volcanism
Famous quotes containing the words forming and/or rocks:
“I heartily wish you, in the plain home-spun style, a great number of happy new years, well employed in forming both your mind and your manners, to be useful and agreeable to yourself, your country, and your friends.”
—Philip Dormer Stanhope, 4th Earl Chesterfield (1694–1773)
“However patriarchal the world, at home the child knows that his mother is the source of all power. The hand that rocks the cradle rules his world. . . . The son never forgets that he owes his life to his mother, not just the creation of it but the maintenance of it, and that he owes her a debt he cannot conceivably repay, but which she may call in at any time.”
—Frank Pittman (20th century)