Well tumbled Natural Smoky Quartz Crystal Stone (small size pieces) - 0.2 Kg Lot (0.44 pound)

Weight per piece: 1.0 to 9.2 gram

Sizes:  5x10x13 mm to 12x18x22 mm (0.2x0.4x0.5 to 0.5x0.7x0.9 inch)

Quantity: about 32 to 82 pieces in each lot

These stones are from Brazil.

The pictures in the listing is just for reference as we are selling multiple pieces with same pictures.

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Smoky Quartz

Smoky or smokey quartz is a brown to black variety of quartz.[1] Like other quartz gems, it is a silicon dioxide crystal. The smoky colour results from free silicon, formed from the silicon dioxide by natural irradiation.

A very dark brown to black opaque variety is known as morion.

The color of smoky quartz is caused by irradiation and traces of aluminum built into its crystal lattice. Aluminum replaces silicon to form a [AlO4]- group instead of [SiO4]. To compensate for the imbalance of charge in the lattice, small monovalent cations (H+, Li+ or Na+) are built into the lattice, as well. High energy radiation transfers the extra electron from [AlO4]- to the cation, and a color center is formed. Interestingly, H+ seems to interfere with this process, and higher concentrations of built-in hydrogen inhibit the formation of color-centers. In normal geological environments this process can only take place at temperatures below 50°C, otherwise the rate of color center destruction surpasses that of color center formation. So the color of the crystals appeared long after the crystals have grown. It is estimated that it takes several million years for a crystal to assume a deep color in a granite of average composition.

The color of smoky quartz is typically much more homogeneous than that of amethyst, but often still more intense at the tips of the crystals. Crystals that show a zonar or patchy coloration are not uncommon, however, and often these are most intensely colored at the edges between the rhombohedral faces. Sometimes a dark color is caused by impurities like organic compounds or manganese oxide, but those rocks should not be called "smoky quartz". That name is reserved for quartz whose color has been induced by radiation.

True smoky quartz will loose its color when heated to about 200°C, and the color will occur again when the crystal is irradiated with x- or gamma-rays. Some (but reportedly not all) smoky quartz is sensitive to ultraviolet light and will pale when exposed to sunlight for a long time. It is not as sensitive as amethyst, though.

Smoky quartz basically appears in the same crystal habits (e.g. long- or short-prismatic, platy, as scepters, with trigonal habit, or as skeleton quartz), and crystal forms (determined by the type of crystal faces that appear on a crystal) as rock crystal. Skeleton quartz and needle quartz seem to be an exception, they both are fast-growing forms and the latter in particular for some reason in most cases doesn't darken upon irradiation. A growth form that is very often smoky is the gwindel, because these apparently only grow in igneous and highly metamorphosed rocks, and usually grow very slowly.

Smoky quartz is usually found in intrusive igneous and certain high grade metamorphic rocks, like granite and orthogneiss, as these contain traces of radioactive elements whose radiation cause the coloration.

Natural smoky quartz comes from many sources around the world. A few of the more noteworthy locations include Brazil, the world's largest supplier.