The word porphyry signifies a rock having as a base a compact mineral substance in which crystalline granules of either another or the same mineral are disseminated. Each porphyry takes its mineralogical name from the substance of which the base is composed, thus it is said to be porphyry of a feldspar base, a syenite base, or an obsidian base, and so on with other substances. When these crystals are small and round the name of porphyry is retained by the stonecutters, when they are large, and square it is called serpentine (serpentine); which is why I divide them into two classes, the porphyries correctly so-called, and the porphyries commonly called serpentines.[p192]
Porphyries correctly so-called (Porfidi
§ I Ancient porphyry (Porfido antico, Marmor porphyrite)
Although porphyry is found in many colours, nevertheless the most common one, but the most beautiful, is that which has a red ground and small white markings. This type, which almost resembles the colour purple, not only gave its name to the stone but also to the city near its quarry that was called Porphyrites (Porfirite). Pliny 105 says that red porphyry was extracted from Egypt, Aristides 106 would have it extracted from Arabia. Stephanius 107 reconciles this difference of opinion by placing the city of Porphyrites on the boundary between Arabia and Egypt, from which it can be deduced that the first quarries of red porphyry were opened near the isthmus of Suez. Another active quarry of porphyry in the Thebaid was mentioned by Eusebius of Caesarea 108 [p193] , thus many ancient writers have called this kind of stone Theban marble (marmo Tebano). Although the utilisation of porphyry may well have been have been initiated late in Rome, since there is no reference to it before the Principate of Claudius, nonetheless it was transported in such quantities that it acquired the name of 'Roman' marble for its excellence (marmo 'Romano' per eccellenza). Codinus 109 tells of a letter from the widow Marcia in which she advises Emperor Justinian that she has sent him eight 'Roman' columns to decorate the temple of S. Sofia; and Cedrenus 110 says that Constantine the Great was buried in a tomb of 'porphyry', otherwise 'Roman' marble.
783. (193.1) Porfido rosso. Deep red ground with small white crystals. The largest masses of this stone to be seen in Rome are the two large columns in S. Giovanni in Fonte, another two in the church of S. Crisogno in Trastevere, and the tazza and the urns of the [p194] Vatican Museum. The four half columns of the High Altar in S. Agnese fuori le mura, are of the most beautiful type. (Rare).
784. (194.2) Another with a purplish ground and few white crystals. The columns of all the altars of S. Maria ad Martyres, known as the Pantheon, are of this type. (Rare).
785. (194.3) Porfido bastardone. Purplish ground without crystals, with large black markings spotted with white. There is a bust of Berenice of this type, with a head of basalte verde, in the museum of the Villa Albani. (Rare).
786. (194.4) Porfido bigio. Light red ground mixed with grey, with rose coloured crystals. The famous column drum seen in the octagonal courtyard of the Vatican Museum is of this type. (Very rare).
787. (194.5) Porfido verde. Green ground with crystals that are partly greenish, and partly gleaming white. The large urn under the altar of S. Niccola al Carcere Tulliano is of this type. At the house of the marble merchant Signor Pietro Sozzi,[p195] in via della Croce no. 78A, there are two beautiful large tazze of green porphyry for sale. (Very rare).
788. (195.6) Porfido nero with gleaming white crystals. The two columns on the windowsill in the urn room in the Vatican Museum are unique. (Very rare).
§ II Italian porphyries (Porfidi d'Italia)
789. (195.1) Porfido delle Alpi. Ground the red colour of roof-tiles with white crystals. (Not common).
790. (195.2) Porfido delle Alpi. Very light purplish ground and white crystals. (Not common).
791. (195.3) Porfido di Corsica. Black ground, in some places tending to grey, with white, angular crystals. (Rare).
792. (195.4) Porfido delle Alpi. Deep green ground with round, white crystals. (Rare).
793. (195.5) Porfido delle Alpi. Light green ground with white crystals. (Rare).
794. (196.6) Porfido dell'Elba. Reddish ground with white crystals. (Not common).
795. (196.7) Porfido di Svezia. Ground purplish mixed with reddish, with angular white crystals. (Not common).
796. (196.8) Porfido di Siberia. Deep green ground with round white crystals. (Rare).
983. (Suppl. 26.1) Porfido delle Alpi. Deep red ground with crystals of quartz amythest. (Very rare).
984. (Suppl. 26.2) Another from the same place. Coffee coloured ground with white crystals and red ones. (Rare).
985. (Suppl. 26.3) Porfido di Siberia. Deep green ground with crystals of very light green positioned in the shape of a cross.
Porphyries commonly called Serpentine (Porfidi volgarmente detti Serpentini, Marmor Lacedaemon)
Pliny 111 speaking of various marbles says that 'they are not all produced from mines, but in many instances they are found scattered just beneath the surface of the earth; one of the most precious kinds is the green Lacedaemonian marble (marmo verde Lacedomonio), more beautiful and vivid than any other'. Papinius Statius 112 says that the hard rocks of Sparta were green. From this it is deduced that this stone was green, hard, and found widely disseminated. All these conditions combine to persuade us that the [p197] Lacedemonian marble of the ancients corresponds to the green porphyry that is commonly called serpentine. That this stone should be green and hard everyone knows, everyone sees; that it should be found disseminated and not as large rocks is demonstrated by its never being seen in large, or even medium sized blocks, but always as small pieces. Indeed in Rome there is not to be seen either a column, or a bath, or an urn of serpentine: more than this it is worth noting that that the ancients used it for flooring. In fact, one such is the flooring of the Nymphaeum known by the name of Egeria's Grotto. Lampridius 113 recounts that Elagabalus inlaid public squares on the Palatine with Lacodemonian porphyritic marble. Pausanius 114 believed that near Crocee, a village in Laconia, there may have been the quarry of the serpentino, and that it was said that it was extracted as separate boulders, like the stones that are carried by rivers, which demonstrates more than ever that serpentine is found disseminated. Various names have been given to this stone. Strabo 115 [p198] called it 'Taygetan' marble (marmo Taigeto) on account of its being found near the mountain of that name: Sextus Empiricus 116 called it 'Taenarian' (Tenario) because Mount Taenarus is near Taygetus. Martial 117 called it 'Spartan' (Spartano) because Sparta is contiguous with Mount Taygetus: Juvenal 118 called it 'Lacedaemonian', (Lacedemonio) another name by which Sparta is called: Paulus Silentiarius 119 said it was Laconian (Laconio) because Sparta is in Laconia: finally Pliny 120 called it emerald (smeraldo), and says precisely that many Laconian eemeralds were found on Mount Taygetus. This stone differs from porphyry by the singular shape of the markings, otherwise crystals, which are rather long and angular, are arranged in the shape of a star, and more commonly in the form of the cross of St. Andrew.
§ I Ancient serpentines (Serpentini antichi)
797. (198.1) Serpentino, light green, with paler crystals tending to faded yellow. The largest [p199] pieces of this stone that I know are two elliptical bands, six palms long, set in the pilasters before the High Altar of the basilica of S. Paolo, which can still be seen intact, and a round slab, five palms in diameter, placed beneath the ambo of the Epistle in the church of S. Lorenzo fuori delle mura. There are also in Rome two rare, and beautiful, elliptical tables, three palms in length, in the possession of Captain Hely, an Irish gentleman. In small pieces (common).
798. (199.2) Another with a deep green ground, and large crystals of grass green. (Rare).
799. (199.3) Another with a light green ground, and paler, slender crystals placed in the shape of a star. (Rare).
800. (199.4) Another with a black ground, and green crystals. (Rare).
801. (199.5) Another with a dark peachy coloured ground, and green crystals in the shape of a star. (Rare).
802. (199.6) Another with a grass green ground, and crystals of black and of white. (Very rare).
803. (200.7) Another with a purplish ground, and green crystals. (Very rare).
804. (200.8) Another with a ground the colour of copper, and green crystals. Perhaps (unique).
805. (200.9) Another with a grass green ground and paler crystals. Commonly called porfido Vitelli because Signor Giuseppe Vitelli recently found it near Ostia. (Very rare).
806. (200.10) Another with a grass green ground, with crystals of green that shade into faded yellow, with many markings of chalcedony and of sardonyx. (Very rare).
807. (200.11) Another with a grey ground, and white crystals. Perhaps (unique).
808. (200.12) Another with a black ground, and white crystals. (Very rare).
809. (200.13) Another with a black ground, and white crystals. There are two vases of this type in the Galleria de' Candelabri of the Vatican Museum, nos. 1463 and 1508, and a column in S. Prassede in front of the door of the of the Cappella della. S. Colonna. (Very rare).
§ II Italian serpentines (Serpentini d'Italia)
810. (201.1) Serpentino di Cecina in Tuscany. Black ground with white crystals verging on grey. (Rare).
811. (201.2) Serpentino delle Alpi. Black ground with gleaming white crystals. Very beautiful and (very rare).
812. (201.3) Serpentino delle Alpi. Green ground with white crystals. (Rare).