|The Very Highest Quality Quartz Information. . .
Bi-coloured Amethyst Citrine
Quartz is a crystalline rock or mineral composed of silicon dioxide.
It is actually very common, and occurs in many varieties, a number of which are gemstones, some of which are very beautiful and very rare.
Different Groups of Quartz Gemstones
There are a number of different groups of quartz gems, differentiated by their exact composition and crystalline structure. These groups are:-
- Fully Crystalline Quartz
This group includes rock crystal, amethyst, citrine, cairngorm and smoky quartz.
Quartzite is composed of an interlocking mass of quartz crystals with irregular boundaries, produced by metamorphic processes. It may contain small crystals of mica or other iron bearing mineral. This group includes aventurine quartz.
- Cryptocrystalline Quartz
This is a group with microscopically small crystals of quartz embedded in opal, which is itself hydrated quartz. The proportion of quartz to opal varies, and this variation is reflected in differing densities, refractive indexes and other properties. The quartz crystals are in a fibrous form, sometimes running approximately parallel to each other, sometimes entwined.
All quartz in this group is a form of chalcedony or agate, although the term agate is often used to describe the banded varieties of chalcedony. Many agates are naturally coloured, others are stained for decorative effect. Varieties include chrysoprase, cornelian (carnelian, sard, sardonyx, onyx, plasma, bloodstone, myrickite. There are many differently named varieties of agate depending on their appearance such as moss agate, fossilised wood. and other forms of fossil. Jasper also belongs to this group, and contains impurities which cause heavy pigmentation.
Opal is hydrated quartz which has formed a solidified gel, and itself has a number of different varieties.
Gem Varieties of Quartz
The following are the main gem varieties of quartz. For details of each type, please take a look at their individual pages, where available. Further information about the other varieties will follow when time permits.
Chemical Composition and Name
|SiO2 - Silicon Dioxide
|2.65 - 2.66
Refractive Index (R.I.)
|1.543 - 1.552 to 1.545 - 1.554
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