Polarised light micrograph of Forbach granite from Raumunzach, Murgtal, Black Forest, Germany. This type of granite is part of the northern Black Forest granite massif. Forbach granite is about 305 million years old and is a light, grey to pink coloured two-mica granite. Its coarseness indicates a relatively slow cooling. Biotite (dark) gives this granite its typical structure. Alkali feldspar (orthoclase), which is reddish in colour and gives this stone its typical colour. It has a quartz content of 26 percent, alkali feldspar is 44%, plagioclase 20%, biotite and muscovite 5% each. Opaque minerals and apatite are less than 1 percent and monazite and xenotime just below that. Due to its high quartz content, this granite is highly wear-resistant and chemically stable. Forbach granite is used as floor and stair covering, monuments and facades. Magnification: x30 when printed at 15 centimetres wide.