Typically show b -quartz habit of hexagonal bipyramids. Often euhedral, with rounded corners and resorption embayments. Derived from hydrothermal veins, pegmatites etc. Zoned inclusions and vermicular chlorite are diagnostic. Most metamorphic quartz is polycrystalline, and may show a variety of forms, often with evidence of stretching or flattening.
Grains are often elongate, with crenulate or granulate boundaries and sub-parallel extinction.
Extinction may be straight or undulose. It is not possible to assign many quartz grains to a particular 'type', especially where they are small or monocrystalline. These must be classified as 'common quartz'. Morphology of quartz grains is not an unequivocal indicator of provenance, only a guide to likely sources. Chert contains minute water bubbles which lower RI to 1.53-1.54 and give a brownish appearance in transmitted light and silvery in reflected light.