Quartz, Optical glass, Fluorite, Single crystal

Glass is a hard transparent material whose main component is silicate and carbonate.
Main component is SiO₂ and the percentage of it vary on forms of glass and behavior of glass largely depends on the composition. Refractive index is between 1.45 and 1.96, gravity is from 2.2 to 6.3, liner coefficient of expansion is
0.5 x 10^-6 to 20×10^-6/K, Young module is 5×104 to
9×104MPa and Mohs hardness is 5 to 7.

Material used for optics parts is referred as optics material and the most widely used optics glass is higher quality than other glass and it needs to have demand refractive index, and striae and air are over certain standard.