Gemstones | Topaz

Topaz Gemstones

Source: Brazil, Czech Republic, Italy, Japan, Mexico, Nigeria, Norway, Pakistan, Sri Lanka, USA

Birthstone: November (Alternate: Citrine)

The name "Topaz" (Topaze French, Topas German, Topacio Spanish) is derived from the Greek "Topazos" or "to seek" (the name of an island in the Red Sea). Topaz is a silicate or "Nesosilicate" mineral created from a combination of aluminium and fluorine. Pure topaz is transparent but is usually tinted by it's impurities. Topaz can be found in a variety of colors ranging from honey-yellow to a deep red-wine color. In the Middle Ages the word "topaz" was used to describe any yellow colored gemstone. The principal source of Topaz (especially red or cognac topaz) is located in the region of the colonial city of Ouro Preto in Minas Gerais, Brazil.

In a case of misidentification, the "Braganza Diamond" set in the Portuguese Crown Jewels was actually a 1,680 carat colorless topaz, and during the Middle Ages, yellow topaz exchanged names with chrysolite. Topaz has good clarity and very few inclusions that are visible to the naked eye (eye clean). Pakistan is one of the few locations producing natural Pink topaz. Pink topaz that was not mined in Pakistan, is usually the result of heat-treatment.

Imperial Topaz

Imperial Topaz with its distinct peach, pink, or mauve hues is perhaps the rarest topaz variety, and the primary source is found in the Ouro Prêto mines of Minas Gerais, Brazil. Imperial Topaz (aka "precious topaz") was named in honor of the Brazilian monarchy who prized its luxurious golden-sherry hues.

Topaz has a hardness of 8 on the Mohs scale and is the hardest silicate along with beryl (Aquamarine). The Toughness of Topaz is Fair. Topaz crystallizes in the orthorhombic crystal system, with an "Elongate Prismatic" crystal habit. Pinacoid, multiple domes and orthorhombic pyramid faces produce complex and multifaceted terminations that are well formed. Topaz has a chain-like lattice structure of irregular octahedrons. Topaz has perfect (easy) basal cleavage in one direction (in the plane perpendicular to the c-axis), with a conchoidal fracture, therefor it is a difficult stone to set without fracturing. Topaz has a refractive index of 1.610 to 1.630.

Photo (left) - resourcescommittee.house.gov

Topaz is usually found in association with more acidic rocks of the granite and rhyolite family. In Brazil, topaz is found in conjunction with Aquamarine and Beryl, and Quartz, within igneous rock pegmatite veins or dikes. Due to it's basal cleavage, topaz should be handled with care to avoid developing cleavage flaws. Topaz is a biaxial mineral with two optic axes that do not line up with the c-axis.

Chemical composition: Al₂SiO₄(F,OH)₂

One of the largest faceted topaz gems in the world is a 93.6 carat Imperial Topaz (Smithsonian Institution collection) found in the Capão Imperial Topaz Mine in Ouro Preto, Brazil.

Topaz Color Enhancements

Blue Topaz

Blue Topaz is very rare in nature. Usually, blue topaz has had a combination of gamma-ray irradiation via an electron-beam linear accelerator, followed by heat treatment at 180º C to 280º C to bring out the cobalt blue color. "Blue" Topaz starts out as a grey-blue to silver-gray colored stone. Blue Topaz is categorized as: "London Blue" (blue-green), "Sky Blue" (light blue), "Swiss Blue" (medium to dark indigo blue), and "Maxi Blue" (deep and intense blue). When yellow topaz is heat treated, it takes on a reddish-pink color.

Orange-brown Topaz is heat treated to 450 C to bring out a purplish-pink color (pinking). These treatments are permanent and do not affect the stone's durability or hardness.

Vapor Color Coating

Iridescent colors such as "Mystic Topaz" can be added to natural topaz by applying a thin layer of titanium oxide vapor (vapor color coating) to the outside of the stone. The vapor color-coating treatment is not permanent and can wear off over time.

Diffusion Topaz Treatment

White, or clear topaz can be treated using "Diffusion Topaz Treatment" which will create "Peacock Blue", "Sapphire Blue", "Apple Green", and "Emerald Green" colors. The diffusion treatment is claimed to be more durable than vapor color-coating. Much of this type of treatment is done in Sri Lanka. A relatively new name on the color-treating front is the so-called "Center-Fussed Colored Topaz".