A native metal, Cu, found in hydrothermal and metasomatic deposits.
Feldspars are the most common minerals in the Earth's crust.
A rock which contains silica in excess allowing the formation of quartz in its mineralogical assemblage. The concept of silica-saturation is mainly applied to igneous rocks, sometimes to metamorphic rocks, hardly ever to sedimentary rocks. The phenomenon by which minerals coloured in thin section exhibit a variation in colour when rotated in plane polarised light. The polarised light vibrates parallel to one of the microscope cross wires and at right angles to the vibration plane of the analyser. Silicates characterised by a three-dimensional framework of silica tetrahedra with all four oxygen atoms shared.