Porphyry

Porphyry is an exceptionally hard mineral of varying colour. Commonest are reddish and greenish porphyries with the inclusions of feldspar, quartz and other minerals.

In Ancient Egypt and Rome porphyry was used for facing slabs, columns and other large details of palaces and temples. In Russia the mineral came into widespread use in the 18th century when St Petersburg was being built.