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

• 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

• 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.

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