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Quartz, Number One Bead Mineral

Quartz (silicon dioxide) is the most abundant free mineral on Earth and a major rock former. The sands of beaches and deserts, gravel on roads, sandstone cliffs and much more is made of quartz. It is also the major ingredient in most glass.

With a hardness of seven it is durable and suitable for gem use. It comes in a bewildering variety of colors and patterns. It is the premiere mineral for beads. Quartz is divided into four subvarieties:

Crystalline quartz forms large, visible crystals. Its hardness is 7 and, in fact, is the type mineral for H7 on the Mohs scale of hardness. It is transparent or translucent.

Chalcedony has tiny crystals that can be seen only with powerful microscopes. They are arranged in "strings," so it is fibrous microcrystalline quartz. It is translucent with a hardness of 6.5. It includes the agates and is the most widely used quartz mineral for beads.

Jasper also form microcrystals, but in grain-like forms and is granular microcrystalline quartz. It is opaque with a hardness of 6.5. Plain jasper is called flint or chert (shown).

Opal crystals are spherical, a fact not known until rather recently. It absorbs water and its surface refection denotes precious opal (common opal does not have the play of colors). It breaks easily and is not widely used for beads. Its hardness ranges from
5 1/4 to 6 1/4.


There are many varieties of each of these and there are ways to alter them.

Plain crystalline quartz is called rock- or quartz crystal. One of the most used quartz varieties is purple amethyst (left). In the center is pink-colored rose quartz. Quartz may also include other minerals, making different varieties. At right is tiger-eye in which the quartz has replaced asbestos fibers.

Chalcedony is usually gray or white. Colored varieties also exist, such as this rather rare blue chalcedony (center). The chalcedony variety most widely used for beads is the red carnelian (right)

As seen below, there is yellow, red and green jasper. Plain jasper is called flint or chert. One variety (far right) is green with flecks of red, known as bloodstone.

Of all the groups of quartz minerals, the most complex and variable are the agates. Agates are chalcedony with structures, either of included materials or internal banding. There are many varieties; over 300 names are widely used.

A sliced and polished piece of banded agate. It was formed when superheated water saturated with silica poured into a cavity in a lava flow. The point of entry can be seen at the top of the stone. Slightly different chemical compositions made for differences in the bands in color, opacity and porosity. At the center, where the melt cooled more slowly, tiny quartz crystals developed. This is called druze.

Historically the most important agate variety is known as Baba Ghor Agate or babaghoria
It comes from the agate mines of Ratanpur, India.

Named for the patron saint of the industry, the term has been in use for hundreds of years. The gray and white banding is not exclusive to the region, but the large amount of it and long exploitation make it an important variety.

On the right is an agate variety called "moss agate." It does not actually contain moss, but iron (black), manganese (red) or chlorite (green) crystals.

Many people are surprised to learn that several of the most famous quartz varieties are always, or nearly always, altered into their gem state by humans.

Thanks, Sindi


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