How many ways can the igenous rock form?

Question

How many ways can the igenous rock form?

Answer 1

One way.  Molten rock cools.

If the molten rock cools slowly underground it is called intrusive.  That means that they intrude into a volume that already has solid rocks.

If the molten rock (or rock materials like ash) get ejected from the bowels of the earth (or undersea) and cool very fast they are extrusive igneous rocks.

In both cases, cooling of the molten rock causes igenous rock to form.

Answer 2

Basically two ways.

Intrusive igneous rock is formed when magma cools and solidifies beneath the surface of the earth.  These rocks are also called plutonic rocks.  They are characterized by a coarse grained texture.  The slower the magma cools the larger the formed crystals will be, hence the coarse grain.  Some magma begins to cool slowly underground and start to form large crystals.  Then due to tectonic processes the partially solidified magma is transported to earth's surface where it cools quickly and forms small crystals.  This is termed porphyritic texture.

Some intrusive igneous formations are laccolith, batholith, stock, sill, and d**e.

Extrusive igneous rocks are formed on the surface of the earth.  These rocks are formed as a result of a volcanic eruption.  Most have a fine grained texture made of small crystals due to rapid cooling.  However, some of the lava cools so quickly that no crystals have time to form.  An example of this type of rock is obsidian, commonly called black glass or volcanic glass.