Igneous Rocks

Igneous rocks are rocks that are formed by cooling lava. It forms when magma ha

Lava

Lava is magma that has escaped from the Earth’s mantle through a volcano, vent, or diverging plate boundary. The viscosity and color of lava depends on the temperature and composition of the

A'a Lava

Pahoehoe Lava

magma. When lava comes out of the earth, it can take multiple forms, though the most common ones are "pahoehoe" and "a’a". Pahoehoe lava is very smooth, almost completely liquid, and cools very quickly.

Types of Igneous Rocks

Basalt, an extrusive igneous rock.

Extrusive/Volcanic

Extrusive or Volcanic is used to define rocks created by magma erupting or flowing from the mantle. These rocks can only be formed when the lava cools for at least five days. This allows time for minerals to be created in the rock and make for a fine-grained texture. Otherwise, the lava would become volcanic glass. An example of an extrusive rock is basalt.

Intrusive/Plutonic

Intrusive or Plutonic rocks are formed when magma crystallizes in the mantle. These rocks can be characterized by their large crystal shapes. The cooling process for these rocks can last days or even weeks. This allows time for crystals to form in the rocks. If a rock shimmers, it is probably intrusive. This can be seen in granite.

Granite, an intrusive igneous rock.