Clinkstone

Clinkstone, or PHONOLITE, is a greenish gray or brownish compact or very finely crystalline igneous rock, remarkable for its tendency to split into slabs, which are now and then thin enough to be used for roofing purposes. This structure is due to the parallel arrangement of plate-like or tabular crystals of sandine felspar. The slabs give a metallic ring or 'clink' when struck with a hammer, whence its name. Its essential mineral components are sandine and nepheline, but other minerals, such as augite or hornblende, leucite and magnetite, are usually present. The rock has often a porphyritic structure.