Geologically, diorite is a dark-gray or greenish igneous rock, consisting chiefly of feldspar and hornblende. Egyptologists, however, misapplied the name diorite to rocks from Chephren's quarry, 65 kilometers (40 miles) northwest of Abu Simbel on the Nile. This quarry is named after the fourth dynasty king Khafre (Chephren, in its Greek form), who used the rock for six statues found in his valley temple at Giza (the site is also sometimes called the Tushka or Gebel el-Asr quarry). The so-called Chephren's diorite is misnamed and actually comprises two varieties of the metamorphic rock called gneiss: the first is a greenish-black and light-gray banded gabbro gneiss, which was used primarily for royal statuary during the fourth, fifth, and sixth dynasties, as well as in the twelfth; the second is a light-colored anorthosite gneiss, with greenish-black streaks and patches in a light-gray matrix, which was used primarily for small vessels in the late Predynastic period and in the first through sixth dynasties. In ancient Egypt, this gneiss was called mntt. In bright sunlight, the rock has a bluish glow that probably attracted quarrying, because of its iridescence (this quality is not seen under the indoor lighting of museums, however).
A true diorite was also used in ancient Egypt, the exceptionally coarse-grained, pegmatitic rock from Wadi Umm Shegilat in the Eastern Desert. This rock consists of greenish-black crystals of hornblende, up to several centimeters in length, set in a light-gray to pale-pink matrix of plagioclase feldspar. It was widely employed for small vessels and occasionally for animal figurines from the late Predynastic period through the Old Kingdom. Such objects are commonly misidentified in the older Egyptological literature as composed of porphyry. The same diorite quarry was used by the Romans during the first two centuries CE. They exported it from Egypt and used it for small columns, basins, pedestals, wall tiles, and pavement tiles. Partially worked materials in the quarry were all dated to the Roman period—stone blocks with saw marks that are not found in any other Egyptian quarry. The extreme coarse grain of the diorite there may have caused the Romans to use saws in shaping the blocks, rather than chisels and picks, as was done in other quarries. The Wadi Umm Shegilat quarry was rediscovered about 1950, but the rock it supplied has long been known from both Roman and later buildings outside Egypt, especially those in Italy, where it is called granito della colonna (“granite of the column”), after one particular pillar in the Basilica of Saint Prassede in Rome. The Roman and earlier Egyptian names for this rock (true diorite) are unknown.
Other igneous rocks with compositions similar to and gradational with that of diorite were worked by the Romans in the Eastern Desert. These include (1) quartz diorite, from quarries in Wadi Umm Balad, near Mons Porphyrites (Ar., Gebel Dokhan), and in both Wadi Barud and Wadi Fatiri el-Bayda, near Mons Claudianus; (2) gabbro, from quarries in Wadi Umm Wikala, near Wadi Semna, and in Wadi Maghrabiya; and (3) granodiorite, from a quarry at Bir Umm Fawakhir, near Wadi Hammamat and Wadi el-Sid. Yet another granodiorite was quarried from the early dynastic through Roman times—the so-called but misnamed black granite, from Aswan.
- Aston, Barbara G. Ancient Egyptian Stone Vessels: Materials and Forms. Studien zur Archäologie und Geschichte Altägyptens, 5. Heidelberg, 1994. Discusses the use of gneiss and diorite for small vessels.
- Aston, Barbara G., James A. Harrell, and Ian M. E. Shaw. “Stone.” In Ancient Egyptian Materials and Technologies, edited by Ian M. E. Shaw and Paul T. Nicholson. London, 1999. Offers an up-to-date summary of the petrology, uses, and sources of all igneous and metamorphic rocks used in ancient Egypt.
- Brown, V. Max, and James A. Harrell. “Topographical and Petrological Survey of Ancient Roman Quarries in the Eastern Desert of Egypt.” In The Study of Marble and Other Stones Used in Antiquity—ASMOSIA III, Athens, edited by Yannis Maniatis, Norman Herz, and Yannis Bassiakos, pp. 221–234. London, 1995. Provides a comprehensive survey of Roman quarries in the Eastern Desert.
- Harrell, James A., and V. Max Brown. “Chephren's Quarry in the Nubian Desert of Egypt.” Nubica 3.1 (1994), 43–57. Describes the results of a recent survey of Chephren's (Khafre's) quarry, with emphasis on the rocks it supplied; gives a complete bibliography of all the earlier work at the site.
James A. Harrell