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Petrographically speaking, porphyry consists of a microcrystalline to vitreous groundmass, which makes up over 65% of its volume, containing up to 30-35% of small crystals. The most abundant crystals consist of quartz, which explains why this rock is also known by the name of “quartz porphyry”.
Porphyry is a type of effusive volcanic rock that is widely spread on Earth’s crust – it can be found both naturally stratified and in monoliths – and it is used for:
- pavings and claddings
- finishing elements
- interior design.
In Italy, in the Trentino-Alto Adige region, there is a considerably thick formation of porphyry, the origins of which date back to 260 million years ago.
Trentino-Alto Adige’s porphyry is of slabs formation: the rock locally features close sub-vertical fracturing along mainly parallel planes, which divides the rock into slabs of thickness varying from a few centimeters to several decimeters. It is thanks to this natural slabs formation that it is possible to obtain products with natural cleft surface, with no need of other kinds of finishings.
The most common colours of this kind of porphyry vary from mixed grey (Colour A) to mixed red/brown (Colour C).