Porphyry (geology)
Porphyry (/ˈpɔːrfəri/ POR-fə-ree) is any of various granites or igneous rocks with coarse-grained crystals such as feldspar or quartz dispersed in a fine-grained silicate-rich, generally aphanitic matrix or groundmass.
[7] The significance of porphyritic texture as an indication that magma forms through different stages of cooling was first recognized by the Canadian geologist, Norman L. Bowen, in 1928.
[11] Rhomb porphyry is a volcanic rock with gray-white large porphyritic rhombus-shaped phenocrysts of feldspar (commonly anorthoclase) embedded in a very fine-grained red-brown matrix.
[16][17][18] Ancient Egyptians used other decorative porphyritic stones of a very close composition and appearance, but apparently remained unaware of the presence of the Roman grade although it was located in their own country.
[20] The red porphyry all came from the Gabal Abu Dukhan quarry (or Mons Porphyrites)[21] in the Eastern Desert of Egypt, from 600 million-year-old andesite of the Arabian-Nubian Shield.
[27] The scientific members of the French Expedition under Napoleon sought it in vain, and it was only when the Eastern Desert was reopened for study under Muhammad Ali that the site was rediscovered by the English Egyptologists James Burton and John Gardner Wilkinson in 1823.
Porphyry was extensively used in Byzantine imperial monuments, for example in Hagia Sophia[28] and in the "Porphyra", the official delivery room for use of pregnant Empresses in the Great Palace of Constantinople, giving rise to the phrase "born in the purple".
The comparative vividness of porphyry to other stones underscored that these figures were not regular citizens, but many levels above, even gods, and worthy of the respect they expected.
That tradition appears to have been started with Diocletian's porphyry sarcophagus in his mausoleum, which was destroyed when the building was repurposed as a church but of which probable fragments are at the Archaeological Museum in Split, Croatia.
[27] Four presently adorn the facade of the main building of the İstanbul Archaeology Museums,[34] including one whose rounded shape led Alexander Vasiliev to suggest attribution to Emperor Julian on the basis of Constantine Porphyrogenitus's description.
Vasiliev conjectures that the nine imperial sarcophagi, including one which carries a crux ansata or Egyptian cross, were carved in Egypt before shipment to Constantinople.
[36] The tomb of Peter III of Aragon, in the Monastery of Santes Creus near Tarragona, reuses a porphyry tub or alveus, which has been conjectured to be originally the sarcophagus of Late Roman Emperor Constans in his mausoleum at Centcelles, a nearby site with a well-preserved 4th-century rotunda.
[39] The tomb of Napoleon at Les Invalides in Paris, designed by architect Louis Visconti, is centered on the deceased emperor's sarcophagus that often has been described as made of red porphyry although this is incorrect.
[40] The sarcophagus of Arthur Wellesley, 1st Duke of Wellington at St Paul's Cathedral was completed in 1858. and was made from a single piece of Cornish porphyry,[41] of a type called luxullianite, which was found in a field near Lostwithiel.
