How many times per second quartz of a wacht vibrates?
Clay/Mudrock- primarily composed of micas, broken down felspars and sericites. All loosely held together and a series of platy minerals which can slide over each other with ease. A quartz arenite is primarily silica which has a hardness of 7 on the Moh's scale, one of the hardest common minerals, often well cemented by finer grained silica (e.g. a cherty/opaline silica matrix).
