Topaz is an aluminum silicate mineral containing fluorine, and it forms in a wide range of colors. The rarest and most prized is imperial topaz, a golden orange to pinkish orange stone mined near Ouro Preto in Brazil. Most blue topaz sold today is colorless topaz that has been irradiated and heated. Topaz rates 8 on the Mohs scale but has perfect cleavage, so it needs some care in jewelry.
What topaz is
Topaz has the formula Al2SiO4(F,OH)2: aluminum, silicon, oxygen and a mix of fluorine and hydroxyl. The ratio of fluorine to hydroxyl affects its optical properties. Fluorine-rich topaz (typical of colorless and blue stones) has lower refractive indices, around 1.609 to 1.620, while hydroxyl-rich topaz (typical of imperial and pink stones) runs higher, around 1.629 to 1.643.
It crystallizes in the orthorhombic system and forms prismatic crystals with striations along their length. Specific gravity is about 3.5, noticeably higher than quartz. Topaz grows in granite pegmatites and in cavities in rhyolite, both igneous settings described on the igneous rocks and gemstones page. Crystals can be very large; some museum specimens weigh many kilograms.
The name probably comes from Topazios, an island in the Red Sea mentioned by ancient writers. The stone mined there was likely peridot, and for centuries "topaz" was applied to almost any yellow or brown gem.
Colors of topaz
Natural topaz occurs colorless, pale blue, yellow, golden brown, orange, pink, red and, rarely, violet. Color causes differ. Chromium gives pink to red and contributes to imperial colors, while color centers formed by natural radiation give many brown, yellow and blue tones.
- Colorless topaz is common and inexpensive. It is the starting material for most treated blue topaz.
- Brown and sherry topaz were popular in older jewelry. Some brown topaz fades in sunlight, a trait of color centers.
- Pink topaz occurs naturally in small amounts in Pakistan and Brazil. Much pink topaz on the market is yellow-orange Brazilian topaz that has been heated to turn pink.
- Natural pale blue topaz exists but is usually light in tone.
Imperial topaz from Ouro Preto
Imperial topaz describes golden orange, peach, pinkish orange and reddish orange stones. The main source for centuries has been a small district near Ouro Preto in Minas Gerais, Brazil, where topaz has been mined since the eighteenth century. The deposits are weathered veins in which topaz crystals sit in soft clay and kaolin, and miners recover them from hillsides.
The name is often linked to the Brazilian imperial family of the nineteenth century, though the exact origin of the term is uncertain. Russian pink topaz from the Ural Mountains was also tied to the Russian court, and that story is sometimes given as the source of the name.
Imperial topaz often shows strong pleochroism, with different shades of orange, pink and yellow in different directions. Fine stones show a saturated orange to reddish orange with pink flashes. Large clean stones are rare and command high prices. The gems of Minas Gerais page covers Ouro Preto and the state's other gems.
Blue topaz by irradiation
Bright blue topaz became common in jewelry from the 1970s onward. Nearly all of it starts as colorless topaz, which is irradiated to create color centers and then heated to remove unwanted brown and fix the blue. Three main shades are sold:
- Sky blue is light blue, often produced by gamma irradiation.
- Swiss blue is a bright medium blue.
- London blue is a deep, slightly grayish or inky blue, usually made with neutron irradiation in a reactor.
The color is stable in normal wear. Treated topaz that has been irradiated in a reactor must be held until any induced radioactivity decays to safe levels before release, and regulators in countries such as the United States set limits for this. Reputable supply chains follow those rules. The gemstone treatments explained page covers irradiation along with other methods.
Mystic topaz and coated topaz
Mystic topaz is colorless topaz with a thin surface coating, usually applied by vapor deposition, that produces a rainbow iridescence. Other coatings give pink, green or blue colors. These coatings sit only on the surface and can be scratched or worn away, especially on facet edges and on rings. Polishing, harsh cleaners and ultrasonic cleaners can damage them. The coating should be disclosed at sale, and the stone should be treated more gently than uncoated topaz.
Cleavage and durability
Topaz has a hardness of 8, so it resists scratches better than quartz. Its weak point is perfect basal cleavage, a plane at right angles to the length of the crystal along which it can split cleanly. A hard knock in the wrong direction can cause a break. Cutters avoid placing the table parallel to the cleavage plane, and setters avoid putting stress across it. The cleavage in gemstones page explains how cleavage affects cutting and setting.
In practical terms, topaz suits pendants and earrings without concern. In rings worn daily, a protective setting such as a bezel or halo helps. Avoid steam, ultrasonic cleaners and sudden temperature changes, which can open cleavage cracks. Warm soapy water and a soft brush are the safest method.
Topaz and citrine confusion
Because "topaz" was once a general term for yellow gems, citrine has often been sold as "Madeira topaz" or "citrine topaz." These names are misleading. Topaz is harder, denser and has higher refractive indices than quartz. A refractometer reading or a specific gravity test separates them quickly. The how to identify gemstones guide covers the tests.
Sources
Brazil is the leading historic source of fine topaz, including imperial topaz and large colorless crystals for treatment. Other sources include Pakistan (pink topaz from the Katlang area), Russia (Urals), Sri Lanka, Nigeria, Madagascar, Mexico and the United States, where Utah's Topaz Mountain is known for sherry crystals in rhyolite that fade in sunlight.
Birthstone and tradition
Topaz has been the November birthstone since the 1912 American list, now shared with citrine. Some lists also suggest blue topaz for December, and topaz is a traditional gift for the fourth and twenty-third wedding anniversaries in some lists. Medieval European writers attributed protective powers to it, which are folklore covered on the gemstone meanings and folklore page.
Frequently asked questions
Is blue topaz natural?
Natural blue topaz exists but is usually pale. Most bright blue topaz is colorless topaz that has been irradiated and heated, and the color is stable.
What is imperial topaz?
Imperial topaz is golden orange to pinkish orange topaz, mainly from Ouro Preto, Brazil. It is the most prized and costly topaz color.
Is topaz durable enough for a ring?
Topaz is hard at Mohs 8, but its perfect cleavage means a hard knock can split it. Protective settings help for daily wear.
Does mystic topaz wear off?
Yes. The rainbow effect is a surface coating that can scratch or wear away over time, especially on rings.