Rocks
By: Uttami Godha
The Rock Cycle
Igneous- Obsidian
Obsidian is formed when molten rock material cools down. This is also why it is an igneous rock; the lava cools down so rapidly that the atoms can't arrange themselves into a new structure. This is why obsidian is so smooth. Obsidian is usually an extrusive rock. Some place it can be formed are: along the edges of a lava flow, where lava touches water, or when lava cools while airborne.
Metamorphic- Slate
Slate is formed when shale, which consists of clay minerals, is put under low heat and pressure. It is found mostly in mountain areas. Slate is metamorphic because it is formed by another rock, shale.
Sedimentary- Rock Salt
Rock salt is formed from the evaporation of ocean or salty lake water. It is rarely found on earth's surface, except for areas of very arid climate. Rock salt is sedimentary because it is made in the presence of water, whose pieces or sediments are cemented together.