GEOLOGY

Detailed explanation-1: -Extrusive, or volcanic, igneous rock is produced when magma exits and cools above (or very near) the Earth’s surface. These are the rocks that form at erupting volcanoes and oozing fissures.

Detailed explanation-2: -Lava cools to form volcanic rock as well as volcanic glass. Magma can also extrude into Earth’s atmosphere as part of a violent volcanic explosion. This magma solidifies in the air to form volcanic rock called tephra. In the atmosphere, tephra is more often called volcanic ash.

Detailed explanation-3: -Igneous rocks contain randomly-arranged crystals. If the magma cools quickly, the crystals will be large (coarse grained). If the magma cools slowly, the crystals will be small (fine grained). Because igneous rocks are formed from molten rock, they do not contain fossils.

Detailed explanation-4: -Igneous rocks form when magma (molten rock) cools and crystallizes, either at volcanoes on the surface of the Earth or while the melted rock is still inside the crust.

Detailed explanation-5: -When magma cools, it solidifies to form rock which is called “igneous rock". That is deceptively simple, since the solidification process can be very complex. There is a considerable range of melting temperatures for different compositions of magma.