Granite is a soil type defined by Tom Stevenson as ‘a hard, mineral-rich rock that warms quickly and retains its heat. Granite contains 40–60% quartz and 30–40 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. 

Bibliography

Tom Stevenson (2011) The Sotheby’s Wine Encyclopedia 5th Edition by Tom Stevenson (Dorling Kindersley, 2011), p.17-19.