Granite | A soil type defined by Tom Stevenson as ‘a hard, mineral-rich rock that warms quickly and retains its heat. Granite contains 40 to 60 per cent quartz and 30 to 40 per cent potassium feldspar, plus mica or hornblende, and various other minerals. It has a high pH that reduces wine acidity. Thus, in Beaujolais, it is the best soil for the acidic Gamay grape. It is important to note that a soil formed from granite is a mixture of sand (partly derived from a disintegration of quartz and partly from the decomposition of feldspar with either mica or hornblende), clay, and various carbonates or silicates derived from the weathering of feldspar, mica, or hornblende.’
Tom Stevenson (2011) The Sotheby’s Wine Encyclopedia 5th Edition by Tom Stevenson (Dorling Kindersley, 2011), p.17-19.