Strictly speaking, porphyry is not a rock family, but a collective term for igneous rock of volcanic origin that contains individual larger crystals in a fine-grained ground mass. The term phorphyry in the proper sense refers to this characteristic porphyritic structure. However, the term "porphyry" is part of the name of numerous working stones and is extremely common in this sense. It is therefore important to look at the individual rock composition and to seek advice from the manufacturer.
Porphyry is formed in several steps: For example, the crystals known as disseminates usually crystallize within the earth's crust, while the lava mass only cools down on the earth's surface when it emerges, for example during a volcanic eruption. Porphyries are usually composed mainly of quartz with a high proportion of feldspars.
Appearance: Reddish, greyish, brownish, sometimes purple. Porphyry consists of a fine-grained base mass with individual coarse-grained disseminations.
Properties: Porphyry is characterized by frost resistance, abrasion resistance and de-icing salt resistance and is therefore particularly suitable for outdoor use. Porphyries can be polished.
Use in construction: natural stone indoors and outdoors (floors, walls), worktops, crushed stone and chippings.
Examples of porphyries: porphyritic rhyolite (quartz-rich) and porphyritic andesite, trachyte, dacite (each quartz-poor).
Source: bauwion
