Colour, characteristics:

Red to reddish brown, rarely grey or slightly greenish. A light-coloured rock due to its high silica content.

- Light-coloured minerals: 80-100%

Of which:

Feldspar: 40-80%
Of which:

-alkali feldspar: 35-100%

-Plagioclase feldspar: 0-65%

Quartz: 20-60%

Dark minerals: 0-20%

- Minor minerals:

Aegirine, biotite, zircon, apatite, magnetite

Very compact structure. Very resistant to weathering.

Formation:

Through relatively rapid cooling of a rock melt from the Palaeozoic era (quartz porphyry) that has reached the earth's surface. Younger ones are called rhyolite or liparite. Occurs in volcanic dome tops and in widespread blankets.

Locations:

Harz, Thuringia, Saxony, Italy (South Tyrol), France (Vosges), Spain, North Africa

Products:

Used as road gravel, chippings, paving stone, rarely decorative stone.