volcanic, describes the processes and products of volcanic eruptions. The solid volcanic products include recently deposited ash and rocks such as basalt and tuff, together with the soils derived from them. Such materials are very variable in composition, but all involve several silicate minerals (see geology) and are therefore rich in potential soil nutrients. Volcanic rocks are often relatively easily weathered so soils formed from them tend to be particularly fertile (unusually so for vineyards) and most are well drained. The various silicate minerals and the nutrients they yield are identical to those in non-volcanic rocks but anecdote and marketing often claim that vines grown on volcanic soils give something extra to wine.