This page will contain discussion groups about Topaz, as they become available.

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. Suborder Pleurodira. 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. Suborder Cryptodira. 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. Suborder Paracryptodira (extinct)
. 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. While the issue is far from resolved, most scientists now lean towards a Diapsid origin for turtles.

It can be found in the Ural and Ilmen mountains, Czech Republic, Saxony, Norway, Sweden, Japan, Brazil, Mexico, and the United States. Re-analysis of prior phylogenies suggests that they classified turtles as anapsids both because they assumed this classification (most of them studying what sort of anapsid turtles are) and because they did not sample fossil and extant taxa were broadly enough for constructing the cladogram. Topaz is found associated with the more acid rocks of the granite and rhyolite type and may be found with fluorite and cassiterite. All molecular studies have strongly upheld this new phylogeny, though some place turtles closer to Archosauria. 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. More recent phylogenetic studies with this in mind placed turtles firmly within diapsids, slightly closer to Squamata than to Archosauria. It can also be irradiated, turning the stone a light and distinctive shade of blue. However, it was recently suggested that the Anapsid-like turtle skull may be due to convergent evolution rather than to anapsid descent.

When heated, yellow topaz often becomes reddish-pink. Most anapsids became extinct in the late Permian period, except procolophonoids and possibly the precursors of the testudines (turtles). They may also be white, gray, green, blue, or reddish-yellow and transparent or translucent. All Anapsid skulls lack a temporal opening, while all other extant amniotes have temporal openings (although in mammals the hole has become the zygoid arch). Pure topaz is transparent but is usually tinted by impurities; typical topaz is wine or straw-yellow. It was believed that they are the only surviving branch of the ancient clade Anapsida, which includes groups such as procolophonoids, millerettids, protorothyrids and pareiasaurs. Topaz has a hardness of 8, a specific gravity of 3.4-3.6, and a vitreous lustre. Their exact ancestry is disputed.

The fracture is conchoidal to uneven. The first turtles are believed to have existed in the era of the dinosaurs, 200 million years ago. 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. Turtles have a gelatinous substance in their upper and lower shell, called calipash and calipee respectively, the calipash being of a dull greenish and the calipee of a light yellow color. It crystallizes in the orthorhombic system and its crystals are mostly prismatic terminated by pyramidal and other faces, the basal pinacoid often being present. The turtles can take up dissolved oxygen from the water through these papillae, in much the same way that fish use gills. The mineral topaz is a silicate of aluminium and fluorine with the chemical formula Al2SiO4(F,OH)2. These projections, called "papillae", have a rich blood supply, and increase the surface area of the cloaca.

This article is about the mineral or gemstone, for other uses see: Topaz (disambiguation).. Some species have large cloacal cavities lined with many finger-like projections. Mineral galleries. However, aquatic respiration in Australian freshwater turtles is currently being studied. Mindat with location data. Although they spend large proportions of their lives underwater, turtles are air-breathing reptiles, and must surface at regular intervals to refill their lungs with fresh air. Webmineral. In some species, temperature of the egg during development determines whether an egg develops into a male or a female: a higher temperature causes a female, a lower temperature causes a male.

Turtle eggs prepared to eat consist mainly of yolk. Their albumen is white and will not coagulate when cooked because of the protein it contains which is different to that of bird eggs. The eggs of the largest species are spherical, while the eggs of the rest are elongated. Sea turtles lay their eggs on dry sandy beaches.

The oldest tortoise on record is Tui Malila, known to have lived at least 188 years. Turtles generally live a long time; some individuals are known to have lived longer than 150 years. The sizes of turtles vary from a few centimetres (forest and jungle species) to two metres (the leatherback turtle and the Galapagos tortoise). Pond turtles (terrapins) are usually much smaller, while some land terrapins (tortoises) are as large as sea turtles.

Sea turtles grow to large sizes and live in the oceans in the temperate and tropical regions of Earth. Reference the Rheodytes leukops species. Some are known to be able to breathe through their rectums as well. The top part of the shell is called the carapace, the bottom is called the plastron, and the two are connected by a bridge.

All turtles have a protective shell around their bodies. . Some species of turtles are highly endangered. About 300 species are alive today.

The order of Testudines includes both extant (living) and extinct species. in North America) to refer to all members of the order, including tortoises, which are predominantly land-based. The term is sometimes used (esp. The term turtle is usually used for the aquatic species, though aquatic fresh water turtles are also called terrapins.

Turtles are reptiles of the order Testudines (all living turtles belong to the crown group Chelonia), most of whose body is shielded by a special bony or cartilagenous shell developed from their ribs. Superfamily Pelomedusoidea. Superfamily Chelonioidea. Superfamily Kinosternoidea.

Superfamily Trionychoidea. Superfamily Testudinoidea.

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