Difference between revisions of "Topaz"

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[[Image:Imperial4.jpg|left|thumb|250px|Peach Pink Imperial Topaz<br />Photo courtesy of Lembeck Gems]]<br clear="left" />
 
[[Image:Imperial4.jpg|left|thumb|250px|Peach Pink Imperial Topaz<br />Photo courtesy of Lembeck Gems]]<br clear="left" />
  
[[Image:Redimper.jpg|left|thumb|250px|Red Imperial Topaz<br />Photo courtesy of Lembeck Gems]]<br clear="left" />
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Topaz is an aluminium silicate with varying amounts of fluorine (F) and hydroxyl (OH) which replace eachother through isomorphous replacement. Extreme outer limits with only fluorine or only hydroxyl have not been reported.
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<!-- [[Image:Redimper.jpg|left|thumb|250px|Red Imperial Topaz<br />Photo courtesy of Lembeck Gems]]<br clear="left" /> -->
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==Diagnostics==
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===Color===
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Topaz is allochromatic and occurs in many colors.
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* colorless
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* yellow
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* green
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* blue
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* red
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* pink
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===Diaphaneity===
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Transparant
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===Refractometer===
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Topaz with high concentrations of fluorine have a lower refractive index thatn those with high concentrations of hydroxyl.
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===Specific gravity===
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As with the refractive index, the specific gravity changes with high concentrations of hydroxyl and fluorine.<br />
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Hydroxyl causes a lower specific gravity while fluorine raises the specific gravity of topaz.
  
 
==Imitations==
 
==Imitations==
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* [http://www.gia.edu/newsroom/issue/2798/2696/insider_newsletter_details.cfm#2 From Gems & Gemology: A New Imitation of Imperial Topaz]
 
* [http://www.gia.edu/newsroom/issue/2798/2696/insider_newsletter_details.cfm#2 From Gems & Gemology: A New Imitation of Imperial Topaz]
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* ''Gems, Their Sources, Descriptions and Identification'' 4th ed. (1990) - Robert Webster ISBN 0750658568 (6th ed.)

Revision as of 04:35, 2 July 2007

Topaz
Chemical composition Al2(F,OH)2SiO4
Crystal system Orthorhombic
Habit Prismatic with pyramidal/domed terminations
Cleavage Perfect, basal plane
Fracture Sub-conchoidal to uneven
Hardness 8
Optic nature Biaxial +
Refractive index 1.606-1.644
Birefringence 0.008 - 0.010
Dispersion Low, 0.014
Specific gravity 3.49 - 3.57
Lustre Vitreous
Pleochroism Distinct to strong (depending on body color)
Peach Pink Imperial Topaz
Photo courtesy of Lembeck Gems

Topaz is an aluminium silicate with varying amounts of fluorine (F) and hydroxyl (OH) which replace eachother through isomorphous replacement. Extreme outer limits with only fluorine or only hydroxyl have not been reported.


Diagnostics

Color

Topaz is allochromatic and occurs in many colors.

  • colorless
  • yellow
  • green
  • blue
  • red
  • pink

Diaphaneity

Transparant

Refractometer

Topaz with high concentrations of fluorine have a lower refractive index thatn those with high concentrations of hydroxyl.

Specific gravity

As with the refractive index, the specific gravity changes with high concentrations of hydroxyl and fluorine.
Hydroxyl causes a lower specific gravity while fluorine raises the specific gravity of topaz.

Imitations

Recently,2007, yellow-orange-pink flame-fusion corundum is offered in Minas Gerais, Brazil as imperial topaz.

Synthetics

Although topaz is synthesized, the material is not commercially available.

Sources

  • Gems, Their Sources, Descriptions and Identification 4th ed. (1990) - Robert Webster ISBN 0750658568 (6th ed.)