Igneous rocks are crystalline solids which cool from magma: the liquid phase of solid rock. Magmas occur at depth in the crust, and are said to exist in "magma chambers," a rather loose term indicating an area where the temperature is great enough to melt the rock, and the pressure is low enough to allow the material to expand and exist in the liquid state. Many different types of igneous rocks can be produced. The key factors to use in determining which rock you have are the rock's texture and composition.
