Rigid mineral materials, consisting of ultra-pure silica fibers, in the form of machinable slabs or blocks for use in thermal treatment equipment such as ovens, drying kilns or driers, for use as UV radiation, visible and infrared light reflectors and/or for use as thermal insulation in a temperature range that can go from 100° to 1,200°C; rigid mineral materials, consisting of ultra-pure silica fibers, in the form of machinable slabs or blocks for the purpose of reflecting visible radiatio...