SMOKY QUARTZ, the black or brown variety of quartz
- VARIETY OF: Quartz
, SiO 2 .
- USES: Gemstone and ornamental stone.
- COLOR: various shades of black and brown.
- INDEX OF REFRACTION: 1.544-1.553
- BIREFRINGENCE: 0.009
- HARDNESS: 7
- CLEAVAGE: none
- CRYSTAL SYSTEM: trigonal
Smoky quartz is a popular variety of quartz.
It has an unusual color for a gemstone and is easily recognized and is well known by the general public.
Only a few other brown or black minerals are ever cut for gemstones such as
the very rare black beryl,
the very common black tourmaline schorl
or brown corundum.
Smoky quartz is also popular as an ornamental stone and is carved into spheres, pyramids, obilisks, eggs, figurines and ornate statues.
Smoky quartz, a variety itself of quartz, has a few varieties of its own.
- Cairngorm is a variety that comes from the Cairngorm Mountains in Scotland.
- Morion is a very dark black opaque variety of smoky quartz.
- Coon tail quartz is a smoky quartz with an alternating black and gray banding.
- A Gwindel is a smoky quartz cluster of nearly parallel crystals, each
rotated slightly relative to the one beside it.
The color of smoky quartz is variable from brown to black and sometimes smoky gray colored specimens are included as smoky quartz.
The cause of the color of smoky quartz is in question but it is almost certainly related to the amount of exposure to radiation that the stone has undergone.
Natural smoky quartz often occurs in granitic rocks which have a small but persistent amount of radioactivity.
Most smoky quartz that makes its way to rock shops and to some gem cutters has been artificially irradiated to produce a dark black color.
Natural smoky quartz comes from many sources around the world.
A few of the more noteworthy locations include Brazil, the world's largest supplier; Pikes Peak area of Colorado, USA, where it is associated with green amazonite; and the Swiss Alps, which has produced many tons of fine specimens.
Smoky Quartz is only one of several quartz varieties.
Other varieties that form macroscopic (large enough to see) crystals
are as follows:
- Amethyst is the purple gemstone variety.
- Citrine is a yellow to orange gemstone variety that is rare in nature but is often created by heating Amethyst.
- Milky Quartz is the cloudy white variety.
- Prasiolite is the leek-green variety.
- Rock Crystal is the clear, colorless variety.
- Rose quartz is a pink to reddish pink variety.