"Rocks don't have flavors. I'm sorry, but they don't" - Kevin Pogue, rock expert, on terroir.
In many reviews of wines, you will see descriptions that refer to a wine's minerality or earthiness, including mine in the Review of Washington Wines. Does that mean there actually minerals or earth in these wines? The answer is no. One time, I ran across an article about a study at the University of Wales that analyzed numerous wines and determined that the mineral contents were so minuscule as to be imperceptible. Does this throw cold water on the idea of minerality or terroir in wine? The answer to that is also no.
The answer is that while terroir does not impart flavors, it can influence the way grape vines grow, thereby producing wines wth distinguishing characteristics. A wine produced from fractured basalt substrate, for instance, will taste different from one from silt and loam soil. This has do with the way vines grow roots in the deep subsoils. Vines growing stressed through rocky soil will produce different tasting wines than ones grown in gravelly or sandy soil. It is in this way that terroir does have real meaning. This is pretty much the way Geology Professor Pogue has explained it, as I have heard a number of times.
The conclusion is that, while rocks don't have flavors, it is still reasonable to describe wines as being minerals or earthy. So I'll just keep on writing about them in that way.