Felsites (Felspat) - micro-or cryptocrystalline quartz rocks - feldspar (similar to granite) composition. Is a fine-grained mass of acidic volcanic rocks - potassium feldspar (orthoclase) and quartz, sometimes with the contents of plagioclase, pyroxene, biotite, etc. It contains 68-75% SiO2, quartz content of felsites range from dacite (68% SiO2) to rhyolites ( 72-75%). The density is 2200-2400 kg / m³, melting point is 1470-1500 ° C, resistivity is 104 Om • m. Acid-resistance in relation to concentrated sulfuric acid is 98,5-99,3%. The absorption of CaO is 80-120 mg / g of solution. Felsite - Bright microcrystalline rock, usually yellowish or reddish, sometimes - green shades may contain colored inclusions.