Quartzite is rock composed of quartz sand grains. Silicified sandstone, or ‘orthoquartzite’, consists of sand grains fused together with silica. It resembles hardened sugar and some varieties have excellent flaking qualities. Metamorphosed sandstone, or ‘metaquartzite’, is formed when the sandstone is altered by heat and pressure, blending and distorting the individual grains.  Metaquartzite is exceptionally tough but can be percussion flaked into durable stone tools.