Q

Quartz:  A form of silica occurring in hexagonal crystals which are commonly colorless and transparent, but sometimes also yellow, brown, purple,
green, etc. It is the most common of all solid minerals. See also Silica.

Quartzite:  A compact granular rock composed of quartz. It is a metamorphosed sandstone and siliceous cement is often so blended with the quartz
grains as to give the rock a nearly homogeneous texture. Primary material in silica brick.

Quench Crack:  A crack resulting from thermal stress induced during rapid cooling or quenching, or from stresses induced by delayed transformations
some time after the article has been fully quenched.