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Quartz Quartz (crystalline) (SiO2) is an abundant rock-forming mineral. A common variety is milky quartz, which, as its name suggests, is white. Quartz has a hardness of 7, a colorless streak, and a vitreous luster. Quartz has no cleavage but does have a conchoidal fracture (smooth, curved fracture resembling the interior surface of a shell). Where quartz forms well-defined crystals, their shapes are six-sided prisms (typically) with a well-developed point. |
Milky quartz occurs in igneous and metamorphic rocks and is a common vein-filling
mineral.
Quartz is used in the manufacture of glass and as an abrasive (sandpaper), and certain varieties can be used as gemstones.
The milky quartz sample in the Texas Rock Kit was collected from a feldspar/milky-quartz-rich pegmatite in the Llano Uplift and is Precambrian in age.