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Your specimen may be a piece of basalt. Basalt forms when
thin, runny lava erupts from the ground and cools into solid rock. Basalt is
often formed at mid ocean ridges: these are places on the sea bed where two
tectonic plates (the earth's crust is made up of a number of separate plates
called tectonic plates) are moving away from each other. Lava bubbles up in the
gap between the tectonic plates and cools into solid rock, and as more lava
erupts more rock is formed and the plates are pushed further apart. Iceland sits
over the mid Atlantic ocean ridge, and it's land is made up almost entirely of
basalt rock.
A number of igneous rocks from The Potteries Museum &
Art Gallery collections are featured on the Virtual
Store.
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