Porphyry

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

The famous single-coloured - grey-violet and violet - porphyries of the Altai were found in the valley of the Korgon, a fast-flowing mountain river, that in the 18th century could be reached only on horseback. In Russia the mineral came into widespread use in the 18th century when St Petersburg was being built. Rastrelli, Voronikhin, Rossi, Montferrand and other architects used porphyries to make vases, standard lamps and other items that can now be seen in the Hermitage and the imperial summer residences.