Color: base "color" is clear, quartz is usually white or yellowish - due to lattice defects and impurities, but it can take virtually any color,
only deep blue quartz is not yet known.
*)The SiO2 compound is able to produce crystals in other crystal systems too. These are called Crystal Modifications (rhombic tridymite, square cristobalite, cubic melanoflogite, and many other) and have different physical properties.
SiO2, in addition to its chemically individual form (quartz) occurs in more complex compounds, especially silicates. Quartz and silicates together form the majority of all known rocks. 4 milliards (in U.S. English = billions) years ago, they perhaps helped the life to emerge. A few millions years ago, flint pebbles contributed to "humanisation of monkeys". Today, modern technology is based on the silicon made of quartz. It never came out of fashion. It was once considered magical and mystic, and travellers always wore a piece of it, to protect themselves from many intrigues of the world. Today, it helps us counting time, and guiding our actions, cars, and airplanes. It helps us to save the environment. There is no field of human activity, for which the quartz and its relatives would be somehow dispensable. It's current technical applications would be a hundred years ago considered miraculous even by the greatest visionaries. Quartz is a magician. It's miracles, however, reflect the spirit and hard work of mankind.