This rock is dolerite; while dolerite is a common igneous rock, the exact composition varies from locality to locality, so it is possible to say exactly where any given dolerite originated. Preselli bluestone comes only from Preselli in Wales and is the stone used to build Stonehenge 5,000years ago.
The particular forms of pyroxene and plagioclase in this dolerite makes it appear a bluish green.
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