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Topaz

This article is about the mineral or gemstone, for other uses see: Topaz (disambiguation).

Topaz 4 Carat Oval Shape Topaz Gemstone Ring Enhanced with Azotic(r)Treatment Heart Cut Sky Blue Topaz Ring

The mineral topaz is a silicate of aluminium and fluorine with the chemical formula Al2SiO4(F,OH)2. It crystallizes in the orthorhombic system and its crystals are mostly prismatic terminated by pyramidal and other faces, the basal pinacoid often being present. It has an easy and perfect basal cleavage and so gemstones or other fine specimens should be handled with care to avoid developing cleavage flaws. The fracture is conchoidal to uneven. Topaz has a hardness of 8, a specific gravity of 3.4-3.6, and a vitreous lustre. Pure topaz is transparent but is usually tinted by impurities; typical topaz is wine or straw-yellow. They may also be white, gray, green, blue, or reddish-yellow and transparent or translucent. When heated, yellow topaz often becomes reddish-pink. It can also be irradiated, turning the stone a light and distinctive shade of blue. A recent trend in jewelry is the manufacture of topaz specimens that display iridescent colors, by applying a thin layer of titanium oxide via physical vapor deposition.

Topaz is found associated with the more acid rocks of the granite and rhyolite type and may be found with fluorite and cassiterite. It can be found in the Ural and Ilmen mountains, Czech Republic, Saxony, Norway, Sweden, Japan, Brazil, Mexico, and the United States.

Etymology and historical/mythical usage

The name "topaz" is derived from the Greek topazos, "to seek," which was the name of an island in the Red Sea that was difficult to find and from which a yellow stone (now believed to be a yellowish olivine) was mined in ancient times. In the Middle Ages the name topaz was used to refer to any yellow gemstone, but now the name is only properly applied to the silicate described above.

According to Rebbenu Bachya, the word "Leshem" in the verse Exodus 28:19 means "Topaz" and was the stone on the Ephod representing the tribe of Dan.

Topaz is also the birthstone of November.

Example of Heat Treated Topaz-Pink Topaz Pear Cut Ring

References

  • Webmineral
  • Mindat with location data
  • Mineral galleries

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Topaz is also the birthstone of November. Other names for tourmalines:. According to Rebbenu Bachya, the word "Leshem" in the verse Exodus 28:19 means "Topaz" and was the stone on the Ephod representing the tribe of Dan. Ironically the rarest variety, colourless achroite, is not appreciated and is the least expensive of the transparent tourmalines. In the Middle Ages the name topaz was used to refer to any yellow gemstone, but now the name is only properly applied to the silicate described above. In jewellery, blue indicolite is the most expensive, followed by green verdelite and pink rubellite. The name "topaz" is derived from the Greek topazos, "to seek," which was the name of an island in the Red Sea that was difficult to find and from which a yellow stone (now believed to be a yellowish olivine) was mined in ancient times. Tourmaline is used in jewelry, pressure gauges, and specialist microphones.

It can be found in the Ural and Ilmen mountains, Czech Republic, Saxony, Norway, Sweden, Japan, Brazil, Mexico, and the United States. Also, tourmaline is a durable mineral and can be found in minor amounts as grains in sandstone and conglomerate. Topaz is found associated with the more acid rocks of the granite and rhyolite type and may be found with fluorite and cassiterite. Magnesium-rich tourmalines, dravites, are generally restricted to schists and marble. A recent trend in jewelry is the manufacture of topaz specimens that display iridescent colors, by applying a thin layer of titanium oxide via physical vapor deposition. Schorl and lithium-rich tourmalines are usually found in granite and granite pegmatite. It can also be irradiated, turning the stone a light and distinctive shade of blue. Igneous rocks, in particular granite and granite pegmatite and in metamorphic rocks such as schist and marble.

When heated, yellow topaz often becomes reddish-pink. Tourmaline is found in two main geological occurrences. They may also be white, gray, green, blue, or reddish-yellow and transparent or translucent. The meaning of the word "schorl" is a mystery, but it may be a Scandinavian word. Pure topaz is transparent but is usually tinted by impurities; typical topaz is wine or straw-yellow. The word tourmaline is a corruption of the Sinhalese word turamali, meaning "stone attracting ash" (a reference to its pyroelectric properties). Topaz has a hardness of 8, a specific gravity of 3.4-3.6, and a vitreous lustre. It may account for 95% or more of all tourmaline in nature.

The fracture is conchoidal to uneven. The most common variety of tourmaline is schorl, first described by Mathesius in 1524. It has an easy and perfect basal cleavage and so gemstones or other fine specimens should be handled with care to avoid developing cleavage flaws. Some forms of tourmaline are dichroic, in that they appear to change color when viewed from different directions. It crystallizes in the orthorhombic system and its crystals are mostly prismatic terminated by pyramidal and other faces, the basal pinacoid often being present. Crystals may be green at one end and pink at the other, or green on the outside and pink inside: this type is called watermelon tourmaline. The mineral topaz is a silicate of aluminium and fluorine with the chemical formula Al2SiO4(F,OH)2. Bi-colored and multicoloured crystals are relatively common, reflecting variations of fluid chemistry during crystalisation.

This article is about the mineral or gemstone, for other uses see: Topaz (disambiguation).. Rarely, it is colourless. Mineral galleries. Usually, iron-rich tourmalines are black to bluish-black to deep brown, while magnesium-rich varieties are brown to yellow, and lithium-rich tourmalines are practically any color: blue, green, red, yellow, pink etc. Mindat with location data. Tourmaline has a wide variety of colors. Webmineral. At the time it was not realised that schorl and tourmaline were the same mineral.

Brightly coloured Sri Lankan gem tourmalines were brought to Europe in great quantities by the Dutch East India Company to satisfy demand as curios and gems. Tourmaline's unusual electrical properties made it famous in the early 18th century. Due to this effect, tourmaline crystals in collections may attract unsightly coatings of dust when displayed under hot spotlights. Tourmaline crystals when warmed become positively charged at one end and negatively charged at the other.

All hemimorphic crystals are piezoelectric, and are often pyroelectric as well. The deposit was discovered in the 1970s, but is now exhausted. An exception was the fine dravite tourmalines of Yinnietharra, in western Australia. Tourmaline is rarely perfectly euhedral.

Prisms faces often have heavy vertical striations that produce a rounded triangular effect. Tourmaline is distinguished by its three-sided prisms; no other common mineral has three sides. Small slender prismatic crystals are common in a fine-grained granite called aplite, often forming radial daisy-like patterns. Interestingly, the style of termination at the ends of crystals is asymmetrical, called hemimorphism.

Tourmaline belongs to the trigonal crystal system and occurs as long, slender to thick prismatic and columnar crystals that are usually triangular in cross-section. It is a complex silicate of aluminium and boron, but because of isomorphous replacement (solid solution), its composition varies widely with sodium, calcium, iron, magnesium, lithium and other elements entering into the structure. The tourmaline mineral group is chemically one of the most complicated groups of silicate minerals. Mineral galleries Accessed 9/12/2005.

Mindat tourmaline group Accessed 9/12/2005. Tourmaline classification Accessed 9/12/2005. Colorless - achroite (from the Greek for "colorless"). Green - verdelite or Brazilian emerald.

Light blue - Brazilian sapphire. Dark blue - indicolite (from indigo). Rose or pink - rubellite (from ruby). Elbaite subgroup: named after the island of Elba, Italy

    .

    Black - schorl. Schorl subgroup:

      . Brown - dravite (from the Drave district of Carinthia). Dravite subgroup:
        .

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