The colour of porphyry varies from light grey to dark brown. This stone is also called “quartz porphyry” because of the presence of a high concentration of quartz crystals.
The porphyry is an effusive lava rock, consisting of a vitreous or microcrystalline basic paste - 65% of the total material - in which small crystals float, with a variable percentage of 30-35%.
The Etruscans used the porphyry in buildings and works of art, as it is used today as well, thanks to its high level of resistance, shown in the surface hardness, the wear and tear resistance against the most extreme weather conditions and mechanic pressures.
The Romans used the porphyry, called lapis porphyrites coming from Egypt, after they had conquered that country during the reign of August, in the year 31 b.C. The stone was extracted from the imperial mines on the Mons Porphyrites and Mons Igneus (today this mountain is called Gebel Dokhan, west of Hurgada, in the Egyptian eastern desert. This stone is extremely hard and difficult to work. It had already been widely used by the Egyptian sovereigns who loved it above all for its reddish colour, which was often associated with the imperial dignity. The porphyry was therefore used for works ordered by the emperor and the small elite of his family members.