Igneous rocks from volcanoes
Volcanoes are the foundation for igneous rocks. Like a bottle of champagne with a cork in it, liquid rock pools in the magma chamber.
Once you pull the cork, the volcano erupts from the mouth spewing lava. Like wax dripping down the side of a candle, igneous rocks like feldspars form.
So hot lava drips on the side of volcanoes then cools, hardens and become igneous rocks like granite. Igneous rocks can also form deep inside the Earth from magma.
Arguably, the start of the rock cycle begins when molten rock cool from volcanoes. Because without igneous rocks, there wouldn’t be the rock cycle.
Types of igneous rocks
Igneous rocks form after cooling and solidifying from magma or lava. So when molten rock cools, they turn into a solid and become igneous rocks
First, you have to understand the difference between lava and magma. And it’s all about location.
For a volcano when it’s deep inside the Earth, it’s magma. Once it erupts, it’s lava. Then it cools and solidifies. But it matters where it cools and solidifies. For example, the two types are intrusive and extrusive rocks.
Intrusive (or plutonic) igneous rocks form inside the Earth from magma. Magma is hot inside Earth so it cools slowly. When it cools, minerals form slowly. So crystals grow very large for intrusive igneous rocks.
Instead of forming deep inside the Earth, extrusive (or volcanic) igneous rocks cool and solidify on the surface. Because they cool quickly, the crystals are smaller. Some types of extrusive igneous rocks can even have pockets of air bubbles inside them.
Dark igneous rock at rift volcanoes
Hidden beneath Earth’s oceans, underwater volcanoes spew out lava at mid-oceanic ridges (rift valleys).
Because divergent plates move apart from each other at these mid-oceanic ridges, magma flows upwards from the mantle beneath.
When the lava hardens, it becomes dark igneous rock or “basalt” at rift volcanoes.
Because divergent plates fills in the gaps with basalt, oceanic crust turns out to be very young geologically.
Over time, the plates grow at oceanic crust and older rock is pushed away from mid-oceanic ridges.