Main Page | See live article | Alphabetical index


Quartz is the most abundant mineral on earth (about 12% vol.), made of trigonal-crystallized silica (silicon dioxide, SiO2), with a hardness of 7 on the Mohs scale. The typical shape is six-sided prisms that end in six-sided pyramids, although these are often distorted, or so massive that only part of the shape is apparant from a mined specimin. Additionally a bed is a common form, particulaly for sub species such as amythyst, where the crystals grow up from a baserock, and thus only one termination pyramid is present. A geode consists of a hollow pebble (usually an approximatly spherical shape), with a hollow centre lined with a bed of crystals.

Being one of the most common minerals, quartz goes by a bewlidering array of different names. The biggest distinction between types of quartz is between macrocrystaline and the microcrystaline (cryptocrystaline) variaties. Chalcedony is a generic term for cryptocrystaline quartz. The cryptocrystline varieties have very small grains, and thus are at best translucent, and mostly opaque, whilst the clear varities tend to be macrocrystaline.

Although many of the names historically arose from the colour of the mineral, current sceintific naming schemes reffer primarily to the microstucture of the mineral, and the colour is a secondary identifier for the cryptocrystaline minerals, whilst colour is a primary identifier for the macrocrystaline varieties. This does not always hold, however.

Major varieties of quartz {| | Chalcedony || Any cryptocrystaline quartz, although generally only used for white or lightly coloured material, otherwise more specific names are used. |- | Agate || Banded Chalcedony |- | Onyx || Agate where the bands are staight, parralell and consistant in size. |- | Jasper || Opaque chalcedony |- | Aventurine || Translucent chalcedony with small inclusions (usually mica) that shimmer. |- | Tigers eye || Fibrous quartz, exhibiting a colour change effect. |- | Rock Crystal ||clear |- | Amethyst || purple |- | Citrine || yellow |- | Rose quartz || pink |- | Milk quartz, or snow quartz || white, translucent to opaque |- | Carnelian || reddish orange |}

Not all varieties of quartz are natuarlly occuring. Prasiolite, an olive coloured material is produced by heat treatement, and although it does occur natuarlly, most citrine is prepared from amythyst.

Quartz often occurs in granite, sandstone and limestone.

Some quartz crystal structures are piezoelectric and used as oscillators in electronic devices such as quartz clocks and radios.

A non-crystalline(glass) form of quartz, called fused quartz, can also be produced, distinct from typical house glass

See also: list of minerals

Quartz is also the name for a display technology.

External links