The golden color and shine of iron pyrite (which is responsible for its nickname, “fool’s gold”) may grab all the attention. But, there is another element of its appearance that is every bit as dramatic: It’s tendency to form into these incredibly precise, almost machine-like cubes.So how does it do it?
Pyrite, of course, doesn’t always form into such sharply-cut shapes. But, on the occasions that it does, the explanation lies deep in the structure of the of the mineral itself. Pyrite contains both iron and sulphur. As drawn out in the above diagram from Indiana’s Geological Survey, those iron and sulphur molecules join themselves into rigid bonds to create a system of cubic crystals. It’s that isometric structure which then forms the sharp planes and lines that you see in the examples above. Edited from This Chunk Of Fool’s Gold Naturally Formed In These Cubes.