This is a sample of the rock used to make the monument Stonehenge in England. Preseli Spotted Dolerite is a chemically altered igneous rock containing spots or clusters of plagioclase feldspar. It is a medium-grained dark and heavy rock, harder than granite. The bluestones at Stonehenge were placed there during the third phase of construction at Stonehenge around 2300 BC. The majority of them are believed to have been brought from the Preseli Hills, about 250 miles away in Wales.