Hmm ... quartz is a mineral SiO2, silica. Common, found in a wide variety of igneous, sedimentary and metamorphic rocks. The main mineral constituent of sands, opals and Silicon Valley. Hardness 7, erosion and weathering resistant.


Granite is an igneous rock composed of a number of minerals in crystalline form, solidified out of a cooling igneous melt. A prime constituent is the mineral quartz. Other minerals include the feldspars (notably plagioclase and orthoclase), mica. If fresh granite is not sealed, it weathers quite nicely to a fertile soil.


For visual appeal, granite sealed against weathering is far more striking than plain quartz as the mineral assemblage is quite rich in texture and colour.


This is just another geologist's view.