Quartz : is the most common mineral on Earth and has a chemical formula SiO2 >98% with traces of aluminum, sodium, potassium and iron. There are many varieties of quartz and it is a component of almost every rock types.
Quartz is found in a variety of crystals that are often colored by impurities. Some varieties are popular as ornamental stone and gemstones e.g. Amethyst [purple], Citrine [yellow/orange], milky quartz [white], rock crystal [ clear], rose quartz [pink/red] and smoky quartz [ brown/gray]. Other smaller quartz varieties are used as semi-precious stones e.g. Agate, onyx jasper and bloodstone.
Quartz has many commercial applications such as sandpaper, polishing powders, building materials, heat-resistant materials, porcelain, glass, metal casting, radios, televisions, clocks and watches.
Quartzite: is composed of sedimentary rock consisting of rounded quartz grains cemented by crystalline quartz. The quartz grains are fused together forming a hard, weather-resistant rock. Like marble, quartzite comes in many colors [gray, yellow to reddish/brown]. When pure quartzite it is very light in color. Quartzite is used in tiles, floor stones, slabs, pavements, pathways, bathrooms, kitchens and flags.
Abundant quantities of Quartzite are found in Australia, Italy, Sweden and Norway
Sandstone : is sedimentary rock made from quartz and feldspar. In some cases it is bonded together with silica. Sandstone is used principally used in the construction of tiles, blocks, slabs and bricks, flooring, wall cladding, fireplaces and pavements. Colors vary from red, green, yellow, gray and white. Principal occurrences of Sandstone are India, Scotland, Algeria.
The rough chemical composition of Quartzite and Sandstone is 93-94% SiO2, approx 1.5% Fe2O3, 1.5%Al2O3 and 1% Na2O.