Mohs scale hardness: 7
Smoky quartz or also spelled as smokey quartz, is a brown to black variety gemstone belong to the quartz family and it is caused through the natural or artificial irradiation of alumunium –containing rock crystal. In the mineral world these colors are somewhat rare, only a few other black or brown minerals are ever cut for gemstones such as the black diamond, brown corundum, smoky topaz or the very rare black beryl.
Smoky Quartz Color
The oxidation states of impurities in the structure of quartz can be altered by the exposure of transparent quartz to radiation which results in the characteristic colors of the crystal. Subsequent heating reverses this process. Natural crystal tends to be smoky to the base, whereas iradiated tends to have white crystal base next to the matrix rock. If it is so black until you cannot see through it and has a good surface luster, then it is probably irradiated. Natural crystals of smoky quartz are also products of irradiation, but by nature in its own very very slow processes.
Where is Smoky Quartz Found
Natural smoky quartz is formed from slow pressurized processes over many years, mainly occurring as fillings of clefts in large serpentine rock. Rutile inclusions (reddish gold strands of Titanium Dioxide that looked like a tiny hairs or needles) sometimes are found in smoky quartz thus the stones are called rutilated smoky quartz. Sometimes a smoke quartz that contains rutilations is called smoky sagenite rather than rutilated quartz.
The gems are also commonly occur in quartz veins where it crystallize inside rock cavities known as vugs. Smoky quartz also is common in vugs or pockets in pegmatite dikes. It can occur as secondary quartz crystals on cryptocrystaline quartz like agate. These are known as Druzy Quartz, it can form in cavities that form geodes.
You can usually find smokey quartz in intrusive igneous and some high grade metamorphic rocks, like orthogneiss and granite, as these contain traces of radioactive elements. Smokey quartz from volcanic rocks is more uncommon, colorless quartz and amethyst dominate here. Smokey quartz from sedimentary rocks is unusual since their content of radioactive elements is usually very low. There are so many “smoky” quartz reported from sedimentary rocks is actually not smoky quartz, but quartz containing brown or black inclusions.
Smoky Quartz Properties, Characteristics and Inclusions
Smoky quartz often has minute cavity inclusions containing water or carbon dioxide. If there is sufficient number of these minute fluid inclusions, the quartz then becomes opaque and is called milky quartz. Smoky quartz mostly form on a matrix of milky quartz and smoky quartz crystals often grade into milky quartz towards their base.
These cavities often contain both gas and liquid, these inclusions are called as enhydros. These inclusions sometimes can be visible to the naked eye and even may show actual movement of the gas through the liquid.
Sometimes smoky quartz forms with etched pattern of lines, depressions and raised termination's. When these etched termination's are acompanied by plainly visible internal cavities arranged in geometric patterrns related to the crystal structure of quartz, the form is referred to as 'elestial' or skeletal quartz. The internal cavities of this skeletal quartz often contain clay minerals of varied colors, accompanied sometimes by water or carbon dioxide. These cavities can have layered or ribbed aspect and sometimes so pronounced as to make that crystal almost hollow, giving rise to the term skeletal quartz.
There are many different minerals that can form as inclusions within smoky quatz. Some of the important varieties of included quartz for gem use are tourmalinated quartz and rutilated quartz. Other common mineral inclusions in smoky quartz are goethite, chlorite and hematite.
Smoky quartz can also be found as gwindle quartz (name from German "Gwindel", meaning "gewunden" = contorted, twisted, wound), a cluster of parallel crystals each rotate slightlly in relation to one sitting next to it. This twisting is due to the presence of a screw axis in structure of the crystal.
These Scotland’s national gemstones can be easily cut and shaped into fashionable accessories and jewelleries. Smokey quartz can be found throughout the world but most commonly found in Scotland, Africa, Colorado, Brazil and Switzerland.
- Cairngorm: a yellowish brown or grayish brown variety originates from Cairngorm Mountains in Scotland.
- Morion: a deep dark brown to black opaque variety found in Italy.
- Coon Tail: a variety banded with gray and black luster, like the tail of raccoon. Coontail quartz is a local name for smoky quartz variety found at several sites near Magnet Cove, Arkansas, United States.
True smoky quartz will loose its color when the crystal is heated to about 200°C, and the color will occur again if it is irradiated with x- or gamma-rays. Some smoky quartz will turn pale when exposed for a long time to sunlight and are sensitive to ultraviolet light. It is not as sensitive as Amethyst, though.
The smoke quartz is often cooked at high temperatures in order to produce the more profitable yellow orange citrine and normally this process creates darker brownish orange stones which often be confused with the deeper color natural citrine from Brazil. Smoke Quartz has been misleadingly sold as Smoky Topaz. Be careful with some unscrupulous dealers who sell ‘smoky topaz’ (no such gemstone known as smoky topaz), it is probably quartz. To tell the difference between smokey quartz and topaz, run your thumb across the table facet; your thumb will ‘stick’ on the quartz, while topaz is slippery and your thumb will slide across the facet like ice.
It is believed smoky quartz have special properties:
- Provide good grounding and cleansing qualities to the wearer.
- Able to chase away some negative energy and gives endurance.
- Reduce depression and has calming effect.
- Good for our “root” chakra (the one at the base of our spine)- the kidneys, adrenal glands, bones, colon, spine and legs.
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