Quartz

SiO₂

Quartz is one of the most abundant minerals on earth — it occurs as an essential mineral in many igneous, metamorphic, and sedimentary rocks. Quartz can occur alone in veins that cross-cut other rocks. Quartz is generally colorless, but some special varieties like amethyst and citrine occur because of small concentrations of elements like lithium or iron. Quartz has characteristic crystal faces and is quite hard (Mohs scale 7, where diamond is 10); quartz has no cleavage and breaks in conchoidal fractures patterns (like glass).