Basalt Rock


Basalt rock is the most common igneous rock at the Earth's surface. 

But it is not seen much because it covers ocean floors.





It is a dark rock, rich in ferromagnesian minerals such as pyroxene, plagioclase and olivine.

While most often it is very fine grained, it also happens that it is porphyritic, and it can have empty cavities from gas or air bubbles, in which case its texture is vesicular.

 basalt rock
 Basalt columns at Giant's Causeway in northern Ireland. By Lena via Flickr.com


It is mostly known to be extrusive, but it can also sometimes be an intrusive igneous rock.

 basalt rocks
 By Jamie Slomski via Flickr.com

The extrusive version forms from lava flows from shield volcanoes.

 columnar basalt
 By Kris Williams via Flickr.com

The intrusive version is interesting because it forms by partial melting - the process where only part of a rock melts and forms a magma that is then moved upwards.

 basalt columns
 By Xevi V via Flickr.com

Fragments of unmelted rock can be carried to the surface with magma, giving us an opportunity to observe the mantle.













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