Decomposed granite of silica sand, silt particles, and clay. Different specific granite types have differing propensities to weather, and so differing likelihoods of producing decomposed granite. The parent granite material is a common type of igneous rock that is granular, with its grains large enough to be distinguished with the unaided eye (i.e., it is phaneritic in texture); it is composed of plagioclase feldspar, orthoclase feldspar, quartz, mica, and possibly other minerals. The chemical transformation of feldspar, one of the primary constituents of granite, into the clay mineral kaolin is one of the important weathering processes. The presence of clay allows water
Harz granite crystals can be up to 18 mm across. Birkenkopf granite was quarried on the Großer Birkenkopf hill south of Hasselfelde. It is a medium-grained granite with blue-grey coloration. In the quarry 30 to 40% blocks of stone could be used for sawing and 50% of exploitable rock debris could be obtained. The quarry closed in 2009. Birkenkopf granite contains 31.3% quartz, 42.6% alkali feldspar, 20.4% plagioclase feldspar, 5.4% biotite and chlorite as well as 0.3% ore minerals like magnetite, pyrite and hematite. The quarry for Wurmberg granite was situated about 2.5 kilometres north of Braunlage and 250 metres high on