Noun
colorless glass made of almost pure silica
Source: WordNetA very clear and durable quartz glass can be made from pure silica, but the high melting point and very narrow glass transition of quartz make glassblowing and hot working difficult. Source: Internet
On the other hand, quartz glass ( fused silica ) must be heated to over convert, but quickly loses its viscosity and formability if overheated, so an oxyhydrogen torch must be used. Source: Internet