Description:This dark rock, rich in iron and magnesium, was once a lava erupted from a volcano. Dark spots are probably larger mineral grains (phenocrysts) that crystallized in the magma before it erupted. This rock has been slightly metamorphosed by heat and pressure, and is now termed "greenstone".
Representing:Precambrian basement rock of the Canadian Shield, older than 1 billion years.
Where:Shield greenstone south
Original location:Edmonton, Alberta
Estimated mass (tonnes):3