Phtanite is a soil type described by Tom Stevenson (2011) as a ‘dark-coloured sedimentary rock bearing stratas of quartz crystals, found in Savennières and Coteaux du Layon.

Bibliography

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