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 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 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 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 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.