Quartz | A soil type defined by Tom Stevenson as ‘the most common and abundant mineral, quartz is the crystalline form of silica. It is found in various sizes, and in almost all soils, although sand and coarse silt contain the largest amount. Quartz has a high pH, which reduces wine acidity, but quartz that is pebble-sized or larger, stores and reflects heat, which increases alcohol potential.’ Quartz is important in Biodynamics. See Horn silica 501. 

Bibliography

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