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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. 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".[1][2]

This article is about the igneous rock. For other uses, see Porphyry.

The term porphyry is from the Ancient Greek πορφύρα (porphyra), 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.[3] Thus porphyry was prized for monuments and building projects in Imperial Rome 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 aphanites or phanerites, that is, the groundmass may have microscopic crystals as in basalt, or crystals easily distinguishable with the eye, as in granite.

Sarcophagus of Frederick II in Palermo Cathedral, Sicily, made of porphyry

Sarcophagus of Frederick II in Palermo Cathedral, Sicily, made of porphyry

Interior of the de' Medici Cappella dei Principi in Florence (1870s photograph)

Interior of the de' Medici Cappella dei Principi in Florence (1870s photograph)

Sarcophagus of Napoleon in Les Invalides, Paris, made of quartzite with a pedestal of green porphyry

Sarcophagus of Napoleon in Les Invalides, Paris, made of quartzite with a pedestal of green porphyry

Wellington's sarcophagus in the crypt of St Paul's in London made from a single block of luxullianite porphyry

Wellington's sarcophagus in the crypt of St Paul's in London made from a single block of luxullianite porphyry

Modern uses[edit]

In countries where many automobiles have studded winter tires such as Sweden, Finland, and Norway, it is common that highways are paved with asphalt made of porphyry aggregate to make the wearing course withstand the extreme wear from the spiked winter tires.[41]

 – List of rock textural and morphological terms

List of rock textures

 – group of ancient quarries in Eastern Egypt, exploited by Romans

Mons Porphyrites

 – Type of volcanic rock containing large porphyritic crystals of quartz

Quartz-porphyry

 – Ancient Roman sarcophagi

Sarcophagi of Helena and Constantina

Media related to Porphyry at Wikimedia Commons

Pictures of the Mons Porphyrites, Red Sea, Egypt.

at the Wayback Machine (archived May 20, 2008)

Rhomb porphyry lavas

at the Wayback Machine (archived December 24, 2007)

Flash showing rhomb porphyry formation

. Encyclopædia Britannica (11th ed.). 1911.

"Porphyry, in petrology"