finer grain than jasper, and less splintery than hornstone. It was the Lydian stone or touchstone of the ancients. It is mentioned and its use described in the writings of Bacchylides about 450 B.C., and was also described by Theophrastus in his book On Stones (Ancient Greek title: Περὶ λίθων: Peri Lithon), a century later. It is evident that the touchstone that Pliny had in mind when he wrote about it was merely a dense variety of basalt. Basanite (not to be confused with bassanite), Lydian stone, and radiolarite (a.k.a. lydite or flinty slate) are terms used to refer to several types of black, jasper-like rock (also including tuffs, cherts and siltstones) which are dense, fine-grained and flinty / cherty in texture and found in a number of localities. The "Lydian Stone" known to the Ancient Greeks is named for the ancient kingdom of Lydia in what is now western Turkey. A similar rock type occurs in New England. Such rock types have long been used for the making of touchstones to test the purity of precious metal alloys, because they are hard enough to scratch such metals, which, if drawn (scraped) across them, show to advantage their metallic streaks of various (diagnostic) colours, against the dark background. There are, confusingly, not one but two rocks called basanite, one being a black form of jasper and the other a black volcanic rock closely akin to basalt. Add to this the fact that many different rock types - having in common the colour black and a fine texture - have, over the ages, been pressed into service as touchstones and it will be seen that there is ample scope for confusion in this petrology- and mineralogy-related field of study. Gallery References External links