Serpentine+blocks

=Serpentine=

The green rock in the facing stone of this building is called Serpentine. It has many veins and fibres of white-cream coloured minerals running through it, which some people believe look like snakes running through it. What do you think?

Serpentine is an unusual rock. It has a very wild history. Serpentines are generally rocks from the mantle - that's the layer below the crust. The mantle exists about 35 km down under our feet, or around 7 km beneath the floor of the ocean. So, how did it get to the surface where we can mine it, you might ask? When ancient oceans close, some of the crust and mantle in the shrinking ocean gets squeezed onto the continents. As they get squeezed up they are exposed to water which turns them from nice mantle rocks, into greeny serpentines. The pressures generate all the veins you see and the waters help make all the white minerals.

EXERCISE: Can you find any tiny fibres in the veins? Some of the fibres are talc, which is used to make baby powder (talcum powder) Some of the fibres may be asbestos. Asbestos is a natural mineral, and has many uses, though it can be a health hazard if you breath fibres in the air. It is safe when in such a solid rock as a serpentine.

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