Quartz is a generic gemstone from which many of the most popular gemstones come.It is one of the most important and most abundant gemstones on the earth. It has impressive variety. Quartz divides into macrocrystalline and microcrystalline forms.
The latter is Chalcedony -microcrystalline quartz intergrown with moganite - and includes the gemstones onyx, agate, aventurine, carnelian, tigers eye, heliotrope and chrysoprase. Chalcedony and its varieties are opaque gemstones and have no visible crystal formation.
The macrocrystalline forms include the popular gemstones amethyst and citrine, although you would never guess so from their names, plus rock crystal, smoky quartz, rose quartz, lemon quartz and black rutilated quartz. Generally the macrocrystalline forms are transparent or translucent and have visible crystal formation.
Pure quartz or rock crystal, is clear as it has no impurities. It's these impurities that create the many variations of quartz.
Quartz is a hard and durable gemstone with a hardness of 7 on the Mohs Scale. It creates fabulous jewellery of infinite variety.
To learn more about each individual type of quartz, take a look at About Gemstones.