Orthoquartzite Subrounded quartz grains cemented in a matrix of silica. The grain boundaries are clearly marked by the fine grained inclusions. Field of View 2.7 mm, plane light Orthoquartzite Note the variety of orientations present in the randomly oriented quartz grains. Field of View 2.7 mm, crossed polars Block diagram showing the relationship between the crystallographic axes and the indicatrix axes. Optical Properties Colour Pleochroism colourless non-pleochroic Form typically anhedral to highly irregular in igneous and metamorphic rocks.
Detritial grains are are more or less equant.
Optic Orientation optic axis is the c axis. Elongate crystals cut from end to end are length slow. Alteration not readily altered and is very stable in weathering environments. Occurrence one of the most widely abundant minerals, present in a wide variety of environments. Distinguishing Features low relief, low birefringence, lack of cleavage, uniaxial positive.