Author: Anthony Clarke, PhD Student in Applied Geology, Curtin University

During the solstices, thousands gather at Stonehenge on the Salisbury Plain in England to celebrate the monument’s astronomical alignment. The focal point of these festivities is the Altar Stone – the six-tonne sandstone slab that lies flat at the centre of Stonehenge. The ancient society that built this monument, from 3,100 to 1,600 BCE, left no written record. But Stonehenge’s building blocks themselves can help us understand it better. These blocks, or megaliths, are divided into two major categories: sarsen stones and bluestones. The Altar Stone is the largest bluestone. Some bluestones were likely quarried from the Mynydd Preseli in…