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Encyclopedia > Asterism (gemmology)
Asterism on the surface of a blue star sapphire
Asterism on the surface of a blue star sapphire
Asterism as seen in a lab-created blue star sapphire
This article is about the characteristic in some gems. For other uses, see Asterism

In gemmology, an asterism is an optical phenomenon displayed by some rubies, sapphires, and other gems of an enhanced reflective area in the shape of a "star" on the surface of a cabochon cut from the stone. Star sapphire cabochon displaying six-ray asterism. ... Star sapphire cabochon displaying six-ray asterism. ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Asterism has several meanings: In astronomy, it refers to a constellation_like group of stars; see asterism (astronomy) In gemmology, it is an optical phenomenon; see asterism (gemmology) In typography, it refers to a symbol; see asterism (typography) This is a disambiguation page — a navigational aid which lists other pages... Gemology (gemmology outside the United States) is the science, art and profession of identifying and evaluating gemstones. ... An optical phenomenon is any observable event which results from the interaction of light and matter. ... Ruby is a red gemstone. ... Sapphire (from Hebrew: ספיר Sapir) is the single-crystal form of aluminium oxide (Al2O3), a mineral known as corundum. ... A selection of gemstone pebbles made by tumbling rough rock with abrasive grit, in a rotating drum. ... A cabochon or cabouchon is a gemstone which has been shaped and polished as opposed to facetted. ...


A distinction can be made between two types of asterism:

  • Epiasterism, such as that seen in sapphire and most other gems, is the result of a reflection of light on parallel arranged inclusions inside the gemstone.
  • Diasterism, such as that seen in rose quartz, is the result of light transmitted through the stone. In order to see this effect, the stone must be illuminated from behind.
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Common Jewellery Materials

Precious metals
Gold • Silver (Sterling silver) • Platinum  • Palladium An elephant carved in rose quartz, 4 inches (10 cm) long Rose quartz is a type of quartz which exhibits a pale pink to rose red hue. ... A gold nugget A precious metal is a rare metallic chemical element of high economic value. ... GOLD refers to one of the following: GOLD (IEEE) is an IEEE program designed to garner more student members at the university level (Graduates of the Last Decade). ... General Name, Symbol, Number silver, Ag, 47 Chemical series transition metals Group, Period, Block 11, 5, d Appearance lustrous white metal Standard atomic weight 107. ... Sterling silver is an alloy of silver containing 92. ... General Name, Symbol, Number platinum, Pt, 78 Chemical series transition metals Group, Period, Block 10, 6, d Appearance grayish white Standard atomic weight 195. ... General Name, Symbol, Number palladium, Pd, 46 Chemical series transition metals Group, Period, Block 10, 5, d Appearance silvery white metallic Standard atomic weight 106. ...


Gemstones
Diamonds • Rubies • Emeralds • Sapphires • Amethyst • Opals • Topaz • Aquamarine • Tanzanite • Alexandrite A selection of gemstone pebbles made by tumbling rough rock with abrasive grit, in a rotating drum. ... This article is about the gemstone. ... Ruby is a red gemstone. ... This article or section does not cite its references or sources. ... Sapphire (from Hebrew: ספיר Sapir) is the single-crystal form of aluminium oxide (Al2O3), a mineral known as corundum. ... Amethyst is a purple variety of quartz often used as an ornament. ... The mineraloid opal is amorphous SiO2·nH2O, hydrated silicon dioxide, the water content sometimes being as high as 20% but is usually between three and ten percent. ... Topaz is a silicate mineral of aluminium and fluorine with the chemical formula Al2SiO4(F,OH)2. ... Aquamarine Aquamarine (Lat. ... Tanzanite is the blue/purple variety of the mineral zoisite discovered in the Meralani Hills of northern Tanzania in 1967, near the city of Arusha. ... The mineral or gemstone chrysoberyl, not to be confused with beryl, is an aluminate of beryllium with the formula BeAl2O4. ...


Others
Amber • Pearls Amber pendants. ... Freshadama grade cultured freshwater pearls. ...


  Results from FactBites:
 
Asterism (257 words)
In gemmology, an asterism is an optical phenomenon displayed by some rubies, sapphires, and other gems of an enhanced reflective area in the shape of a "star" on the surface of a cabochon cut from the stone.
Asterism is caused by dense inclusions of tiny, parallel, slender fibers in the mineral which cause the light to reflect a billowy, star-like formation of concentrated light which moves around when the mineral is rotated.
This is usually caused by small needles of rutile (titanium oxide) in the case of ruby and sapphire.
  More results at FactBites »


 
 

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