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Porphyry ( ) is any of various or with coarse-grained such as feldspar or quartz dispersed in a fine-grained silicate-rich, generally aphanitic matrix or groundmass. In its non-geologic, traditional use, the term porphyry usually refers to the purple-red form of this stone, valued for its appearance, but other colours of decorative porphyry are also used such as "green", "black" and "grey".BRADLEY, M. (2006). COLOUR AND MARBLE IN EARLY IMPERIAL ROME. The Cambridge Classical Journal, 52, 1–22. http://www.jstor.org/stable/44698291Mari 2015: Z. Mari, “The Marbles from the Villa of Trajan at Arcinazzo Romano (Rome)” in P. Pensabene, E.Gasparini (edited by) Interdisciplinary Studies on Ancient Stone, ASMOSIA X, International Conference (Rome, 2012), Rome 2015
The term porphyry is from the Ancient Greek πορφύρα (), meaning "purple". Purple was the colour of royalty, and the Roman "imperial porphyry" was a deep purple igneous rock with large crystals of plagioclase. Some authors claimed the rock was the hardest known in antiquity. Thus porphyry was prized for monuments and building projects in Roman Empire and thereafter.
Subsequently, the name was given to any igneous rocks with large crystals. The adjective porphyritic now refers to a certain texture of igneous rock regardless of its chemical and mineralogical composition or its color. Its chief characteristic is a large difference in size between the tiny matrix crystals and the much larger phenocrysts. Porphyries may be or , that is, the groundmass may have microscopic crystals as in basalt, or crystals easily distinguishable with the eye, as in granite.
Porphyry can also form even from magma that completely solidifies while still underground. The groundmass will be visibly crystalline, though not as large as the phenocrysts. The crystallization of the phenocrysts during fractional crystallization changes the composition of the remaining liquid magma, moving it closer to the Eutectic system, with a mixed composition of minerals. As the temperature continues to decrease, this point is reached, and the rock is entirely solidified. The simultaneous crystallization of the remaining minerals produces the finer-grained matrix surrounding the phenocrysts, as they crowd each other out.
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.
Porphyritic texture is particularly common in andesite, with the most prominent phenocrysts typically composed of plagioclase feldspar. (1996). 9780716724384, W.H. Freeman. ISBN 9780716724384 Plagioclase has almost the same density as basaltic magma, so plagioclase phenocrysts are likely to remain suspended in the magma rather than settling out.
Rhomb porphyry is found in continental rift areas, including the East African Rift (including Mount Kilimanjaro), Mount Erebus near the Ross Sea in Antarctica, the Oslo graben in Norway, and south-central British Columbia.
It was called "Imperial" as the mines, as elsewhere in the empire, were owned by the emperor.A. M. Hirt, IMPERIAL MINES AND QUARRIES IN THE ROMAN WORLD. ORGANIZATIONAL ASPECTS 27 bc–ad 225. Oxford: Oxford University Press, 2010. isbn 9780199572878 p 368 The red porphyry all came from the Gabal Abu Dukhan quarry (or Mons Porphyrites) in the Eastern Desert of Egypt, from 600 million-year-old andesite of the Arabian-Nubian Shield. The road from the quarry westward to Qena (Roman Maximianopolis) on the Nile, which Ptolemy put on his second-century map, was first described by Strabo, and it is to this day known as the Via Porphyrites, the Porphyry Road, its track marked by the , or watering wells that made it viable in this utterly dry landscape. It was used for all the red porphyry columns in Rome, the on busts of , the panels in the revetment of the Pantheon, the Column of Constantine in Istanbul as well as the altars and vases and fountain basins reused in the Renaissance and dispersed as far as Kyiv.
The Romans also used "Green Porphyry" ( lapis Lacedaemonius,Pliny Nat. Hist., 36,55 from Greece, also known today as Serpentinite),Pensabene P., I marmi nella Roma antica, Rome 2013, pp. 59-62. and "Black Porphyry" from the same Egyptian quarry.Paul T. Nicholson, Ian Shaw, Ancient Egyptian Materials and Technology, Cambridge University Press 2000 p 49
After the fifth century the quarry was lost to sight for many centuries. Byzantium scholar Alexander Vasiliev suggested this was the consequence of the Council of Chalcedon in 451 and the subsequent troubles in Egypt. 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 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".
In general, the renowned rarity and striking appearance of porphyry in the late Roman Empire meant that its use was limited to explicitly Imperial monuments and architecture, thereby helping to emphasize the power and authority of the Emperor in the eyes of the citizens. Porphyry also stood in for the physical purple robes Roman emperors wore to show status, because of its purple colouring. Similar to porphyry, purple fabric was extremely difficult to make, as what we now call Tyrian purple required the use of rare sea snails to make the dye.Schultz, Colin. "In Ancient Rome, Purple Dye Was Made from Snails." Smithsonian magazine. Smithsonian Institution, 10 Oct. 2013. Web. 30 November 2017. http://www.smithsonianmag.com/smart-news/in-ancient-rome-purple-dye-was-made-from-snails-1239931/?no-ist The colour itself reminded the public how to behave in the presence of the emperors, with respect bordering on worship for the self-proclaimed god-kings.Haynes, D. E. L. “A Late Antique Portrait Head in Porphyry.” The Burlington Magazine, vol. 118, no. 879, 1976, pp. 357. JSTOR, JSTOR, www.jstor.org/stable/878411. Retrieved 30 November 2017.
Nine other imperial porphyry sarcophagi were long held in the Church of the Holy Apostles in Constantinople. They were described by Constantine VII in the De Ceremoniis (mid-10th century), who specified them to be respectively of Constantine the Great, Constantius II, Julian, Jovian, Theodosius I, Arcadius, Aelia Eudoxia, Theodosius II, and Marcian. Of these, most still exist in complete or fragmentary form, despite depredations by later Byzantine Emperors, Fourth Crusade, and Ottoman conquerors. Four presently adorn the facade of the main building of the İstanbul Archaeology Museums, 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 Ankh, were carved in Egypt before shipment to Constantinople.
The tomb of Peter III of Aragon, in the Santes Creus near Tarragona, reuses a porphyry Bathtub or alveus, which has been conjectured to be originally the sarcophagus of Constans in his mausoleum at Centcelles, a nearby site with a well-preserved 4th-century rotunda.
In twelfth- and thirteenth-century Sicily, another group of porphyry sarcophagi were produced from the reign of Roger II onward and used for Royal and then Imperial burials, namely those of King Roger II, King William I, Emperor Henry VI, Empress Constance, and Emperor Frederick II. They are all now in the Palermo Cathedral, except William's in Monreale Cathedral. Scholar Rosa Bacile argues that they were carved by a local workshop from porphyry imported from Rome, the latter four plausibly (based on observation of their fluting) all from a single column shaft that may have been taken from the Baths of Caracalla or the Baths of Diocletian. She notes that these Sicilian porphyry sarcophagi "are the very first examples of medieval free-standing secular tombs in the West, and therefore play a unique role within the history of Italian sepulchral art (earlier and later tombs are adjacent to, and dependent on walls)."
Six grand porphyry sarcophagi are featured along the walls of the octagonal Medici Chapels (Chapel of the Princes) that was built as one of two Medici Chapels in the architectural complex of the Basilica of San Lorenzo, in Florence, Italy, for the de' Medici family. Purple porphyry was used lavishly throughout the opulent chapel as well, with a revetment of marbles, inlaid with other colored marbles and semi-precious stone, that covers the walls completely. Envisioned by Cosimo I, Grand Duke of Tuscany (1537–1574), it was initiated by Ferdinand I de' Medici, following a design by Matteo Nigetti that won an informal competition held in 1602 by Don Giovanni de' Medici (a son of Cosimo I), which was altered somewhat during execution by Buontalenti.Touring Club Italiano, Firenze e dintorni (Milan, 1964), p. 285f.
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. Napoleon's sarcophagus is made of quartzite, however, its pedestal is made of green andesite porphyry from Vosges. 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 Cornwall porphyry, of a type called luxullianite, which was found in a field near Lostwithiel.
Use in art and architecture
Antiquity and Byzantium
To the Romans it was known as Lapis porphyrites. Pliny the Elder's Natural History (36, 11) affirmed that the "Imperial Porphyry" had been discovered in Egypt during the reign of Tiberius; an inscription recently discovered and dated from AD 18 mentions the Roman Caius Cominius Leugas as the finder of this new quarry. W. Van Rengen¸"A New Paneion at Mons Porphyrites”, Chronique d'Égypte, vol. 70, issue 139-140, p. 240-245.
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, because its colour had no official value like that of Romans. It was also sometimes used in Minoan art, and as early as 1850 BC on Crete in Minoan Knossos there were large column bases made of porphyry.
Roman and late Roman imperial sarcophagi
A uniquely prestigious use of porphyry was its choice as material for imperial Sarcophagus in the 4th and early 5th centuries. 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. The oldest and best-preserved ones are now conserved at the Vatican Museums and known as the Sarcophagi of Helena and Constantina.
Porphyry sarcophagi in post-Roman Western Europe
The imperial porphyry sarcophagi tradition was emulated by Ostrogothic King Theodoric the Great (454-526), whose mausoleum in Ravenna still contains a porphyry Bathtub that was used as his sarcophagus. Similarly Charles the Bald, King of West Francia and Roman Emperor, was buried at Saint-Denis in a porphyry tub which may be the same one known as "Dagobert I's tub" ( cuve de Dagobert), now in the Louvre.
Modern uses
In countries where many automobiles have studded such as Sweden, Finland, and Norway, it is common that highways are paved with Asphalt concrete made of porphyry aggregate to make the wearing course and withstand the extreme wear from the spiked winter tires. (2025). 9789171589606, Sveriges geologiska undersökning. ISBN 9789171589606
See also
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