In a Li.sub.2OAl.sub.2O.sub.3SiO.sub.2 based crystallized glass using SnO.sub.2 as a substitute fining agent for As.sub.2O.sub.3 or Sb.sub.2O.sub.3, a crystallized glass having less yellow coloration is provided at low costs. The glass is a Li.sub.2OAl.sub.2O.sub.3SiO.sub.2 based crystallized glass comprising from 0.01 to 0.9% of SnO.sub.2 in terms of % by mass and having a content of each of As.sub.2O.sub.3 and Sb.sub.2O.sub.3 of 1,000 ppm or less as a glass composition, which has a V.sub.2O.sub.5 content of from 0.08 to 15 ppm in the glass composition.

An object is to improve quality of a nitride crystal. A crystal represented by a composition formula In.sub.xAl.sub.yGa.sub.1-x-yN (satisfying 0x1, 0y1, and 0x+y1), wherein the concentration of carbon in the crystal is less than 110.sup.15 cm.sup.3, and the concentration of an electron trap E3 that exits in an energy range from 0.5 eV to 0.65 eV from a lower end of a conduction band in the crystal is less than 110.sup.14 cm.sup.3.

A processing method of a single-crystal quartz material includes the following steps. An area to be processed in which the single-crystal quartz material readily generates twin crystals is determined. The area to be processed on the single-crystal quartz material is modified using a modifier, so that a processing difficulty of the area to be processed is reduced. The single-crystal quartz material of the modified area to be processed is processed using a processor.

A processing method of a single-crystal quartz material includes the following steps. An area to be processed in which the single-crystal quartz material readily generates twin crystals is determined. The area to be processed on the single-crystal quartz material is modified using a modifier, so that a processing difficulty of the area to be processed is reduced. The single-crystal quartz material of the modified area to be processed is processed using a processor.