An intrusive igneous rock has larger crystals than an extrusive igneous rock. In an extrusive rock the crystals are usually so fined grained that they are not visible by the naked eye. However, the individual crystals in an intrusive igneous rock can be viewed with the naked eye.
On the surface:
Volcanic lava and ash in various forms - some rubble-like, some with wrinkly surfaces, etc. Very fine crystals possibly too small for the naked eye, thanks to rapid cooling. Also vesicles - rounded cavities that had been gas bubbles, revealed by weathering or artificial cutting.
The SW English city of Exeter is built on the remnants of a volcano, and many of its Mediaeval buildings show rough blocks in their walls of both vesicular lava and a very coarse sandstone breccia.
Polygonal columns that form in flood-basalt lava as it cools - e.g Giant's Causeway, Isle of Staffa (Fingal's Cave).
Pillow lava - from undersea eruptions now revealed on land by uplift.
Plutonic rocks:
More noticeably crystalline - possibly very large but rather irregular crystals (phenocrysts) in granite.
Much more solid appearance to the formation generally, but it may be broken by tension-cracks, and an exposed batholith can spall on a large scale, known as 'onion-skin weathering'.
I have seen a fine example, in Norway, of 'onion-skin' layers about 2 metres high, creating short climbs in progressing up the dome-shaped hill.
Also dykes and sills, possibly in erosion or artificial section, showing entrapped xenoliths in varying stages of dissolution; and in granite, rarely, circles that are the sectioned shells of "orbs".
Metamorphism in country rock at side of intrusion.
Extrusive igneous rock (that was formed after being erupted from a volcano) will have a much smaller crystal size than an intrusive igneous rock.
By its texture.
Extrusive because they are formed outside of the earth's core. Rocks formed below earth's surface are intrusive because they are formed inside the earth's core.
Extrusive igneous rocks are formed
Igneous rock is formed when magma cools and becomes solid.
The molten rock that is found inside the earth is usually simply called magma. It becomes lava after it leaves the volcano at the surface of the earth.
Between 50 and 200 km below Earth's surface
Igneous rock can form inside the Earth or on its surface, from the solidification of molten rock.
Extrusive because they are formed outside of the earth's core. Rocks formed below earth's surface are intrusive because they are formed inside the earth's core.
No. Extrusive igneous rock is formed at or near the surface from rapid cooling. Intrusive igneous rock is formed below the surface from slow cooling of magma.
Extrusive igneous rocks are formed
Extrusive igneous rocks.
Igneous rock formed from cooling magma below the surface is called intrusive igneous rock.
Igneous rock is formed when magma cools and becomes solid.
No. Intrusive igneous rocks are formed beneath the earth's surface when magma cools and extrusive igneous rocks form when lava extrudes from a volcano and cools.
Igneous rocks that form below the Earth's surface are called intrusive igneous rocks (or plutonic).
Volcanoes.
No. A rock formed below earth's surface as magma is an igneous rock.
The molten rock that is found inside the earth is usually simply called magma. It becomes lava after it leaves the volcano at the surface of the earth.