SMOKY QUARTZ

Description:

Smoky quartz is a macrocrystalline variety of the mineral Quartz (SiO₂). Quartz is the most abundant single mineral on earth: it makes up about 12% of the earth's crust, occurring in a wide variety of igneous, metamorphic and sedimentary rocks.

Smoky quartz has an unusual color for a gemstone and is easily recognized and is well known by the general public. Smoky quartz is transparent quartz that is brown, gray or black. It commonly occurs in quartz veins where it crystallizes inside rock cavities known as vugs. 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 persistant amount of radioactivity. Smoky quartz is recognized by its crystal habit, transparency, hardness, glassy luster, color, conchoidal fracture and general lack of cleavage.

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.

Natural smoky quartz comes from many sources around the world. A few of the more noteworthy locations include Brazil, the worlds largest supplier; Pikes Peak area of Colorado, USA, and the Swiss Alps, which has produced many tons of fine specimens. Unique specimens were found in Ural Mountains, Russia.

Smoky quartz has always been used in jewellery, especially for men's signet rings. Only a few other brown or black minerals are ever cut for gemstones such as the smoky topaz, the very rare black beryl or the brown corundum. Smoky quartz is also popular as an ornamental stone and is carved into spheres, pyramids, obilisks, eggs, figurines and ornate statues.

Characteristics:

Chemistry: variety of quartz, SiO₂

Class: tectosilicate

Hardness (Mohs scale): 7

Density: 2.65

Refractive index: 1.54 – 1.55

Dispersion: 0.013

Crystal system: Hexagonal-Rhombohedral

Crystal habit: macroscopic crystals commonly occur as horizontally striated hexagonal prisms terminated by a combination of positive and negative rhombohedrons forming six sided pyramids

Cleavage: none

Transparency: transparent to translucent to opaque