Colour, properties:

Colour grey, grey-green to dark green, green-black. Main constituents are hornblende and plagioclase feldspar; secondary constituents are biotite, chlorite, garnets, epidote, zoisite. Structure usually massive, fine- to coarse-grained. Individual crystals (so-called porphyroblasts) are noticeably larger than the groundmass. Slatey varieties represent transitional members to related rocks. Amphibolite is very strong and weather-resistant.

Formation:

Through intensive transformation (metamorphosis) from rocks low in silica (e.g. gabbro, basalt, diabase) or marls as a result of high pressures and high temperatures. Genetically related to amphibolite is eclogite, which is rare but very decorative due to the red garnets that are always embedded in it.

Locations:

Black Forest, Spessart, Fichtelgebirge, Erzgebirge, Austria (Hohe Tauern), Switzerland (St Gotthard massif), Scandinavia

Products:

Crushed gravel for heavy-duty use. Split grades are used as floor and decorative slabs.