Igneous Rocks
Igneous rocks are formed from molten rock called magma. They are mostly crystalline (made up of interlocking crystals) and usually very hard to break.
Basalt
Basalt is made of fine-grained interlocking crystals (about 1mm in size). It is black or dark grey in colour, and often contains vesicles – bubbles of gas trapped as the lava cooled. Pumice
Pumice is formed when gas-rich magma froths up to form a sort of “mousse”. The lava is glassy-looking and is so full of bubbles that it floats on water! Gabbro
Barry Marsh, School of Ocean and Earth Science, University of Southampton
Gabbro is made of coarse-grained (5mm or so) interlocking crystals. Its overall colour is dark grey but it often contains glassy or pale-coloured crystals of feldspar as well as dark minerals.Granite
Barry Marsh, School of Ocean and Earth Science, University of Southampton
Granite is made of coarse-grained (5mm or so) interlocking crystals. It has more light coloured crystals than dark, usually of white or pink feldspar, glassy quartz, and shiny mica.