Difference between revisions of "Garnet"

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(Online G&G articles on garnet)
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==Meet the family==  
 
==Meet the family==  
  
Admired by mankind as long as history can take us back and available in many colors, garnets have been an important gem material throughout times. Both historical and archaeological research dates the use of garnets as a gem material back to the earliest civilisations on this planet.  
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Admired by mankind as long as history can take us back and available in many colors, garnets have been an important gem material throughout times. Both historical and archaeological research dates the use of garnets as a gem material back to the earliest known civilisations.  
  
 
[[File:Pomseeds2.jpg|thumb|right|150px|Pomegranate seeds, the fruit garnet may derive its name from]]The family has possibly gained its name after the red varieties which resemble the seeds of a pomegranate in color. The term ''garnet'' now stands for a whole family of minerals that crystallizes in the cubic system and shares the same chemical blueprint. The elements used to fill that blueprint make a gem garnet belong to one or more of the following family members:
 
[[File:Pomseeds2.jpg|thumb|right|150px|Pomegranate seeds, the fruit garnet may derive its name from]]The family has possibly gained its name after the red varieties which resemble the seeds of a pomegranate in color. The term ''garnet'' now stands for a whole family of minerals that crystallizes in the cubic system and shares the same chemical blueprint. The elements used to fill that blueprint make a gem garnet belong to one or more of the following family members:
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==Garnet names==
 
==Garnet names==
  
It would have been easy if nature presented us with pure family members. That, unfortunately for those trying to classify garnets, but luckily for you isn't the case. The family members that are listed above represent end members within the garnet group. In other words: their composition is an ideal, theoretical one. In reality all the garnets we use as gem materials are a mix of two or more end members in various ratios. Some of the magnesium which makes a pyrope a pyrope can be replaced by iron, or some of the iron that makes an almandine an almandine is replaced by manganese. In gemology this 'mixing of end members' is called ''isomorphous replacement''. The composition of a garnet determines certain measurable characteristics of the stone such as [[refractive index]] and [[specific gravity]]. It can also influence the color of the stone and that is where you get lucky: garnets come in many colors and shades. The confusion which occurs from these mixed garnets together with marketing strategies have caused an array of trade names to be invented for various garnets. While it is scientifically correct to call the the green garnet found in Kenya a green grossular, you will never encounter it under any other name than Tsavorite. It just sells better that way. Some names are relatively new and are still being contested, others have been in use so long that they have gotten a firm grounding in literature and have been adopted by gemologists. It is important to remember that at the end of the day all garnets are a mix of two or more of the end members mentioned above.
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It would have been easy if nature presented us with pure family members but unfortunately for those trying to classify garnets, this isn't the case. The family members that are listed above represent end members within the garnet group. In other words their composition is an ideal, theoretical one. In reality all the garnets we use as gem materials are a mix of two or more end members in various ratios. Some of the magnesium which makes a pyrope a pyrope can be replaced by iron, or some of the iron that makes an almandine an almandine is replaced by manganese. In gemology this 'mixing of end members' is called ''isomorphous replacement''. The composition of a garnet determines certain measurable characteristics of the stone such as [[refractive index]] and [[specific gravity]]. It can also influence the color of the stone which is why garnets come in many colors and shades. The confusion which occurs from these mixed garnets together with marketing strategies have caused an array of trade names to be invented for various garnets. While it is scientifically correct to call the the green garnet found in Kenya a green grossular, you will never encounter it under any other name than Tsavorite. It just sells better that way. Some names are relatively new and are still being contested, others have been in use so long that they have gotten a firm grounding in literature and have been adopted by gemologists. It is important to remember that at the end of the day all garnets are a mix of two or more of the end members mentioned above.
  
 
{| class="wikitable" style="margin-left:0; width:90%;"
 
{| class="wikitable" style="margin-left:0; width:90%;"
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==Garnets in history==
 
==Garnets in history==
  
Garnets have been used wherever they occur for as long as mankind can remember. From [[Egyptian jewelry|predynastic Egypt]] to the discovery and hype of Fanta orange garnets in Tanzania in 2007, garnets have never ceased to capture our attention. The Roman writer Pliny mentions gemstones called carbuncles, some of which are thought to be garnets. The red family member almandine was a very popular gemstone with the [[Germanic jewelry|Germanic tribes]] which inhabited northern Europe during Roman times. They were used for [[cloisonné]] inlay work of which the items found at Sutton Hoo are a great example.
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Garnets have been used wherever they occur for as long as mankind can remember. From [[Egyptian jewelry|predynastic Egypt]] to the discovery and hype of Fanta orange garnets in Tanzania in 2007, garnets have never ceased to capture our attention. The Roman writer Pliny mentions gemstones called [[carbuncle]]s, some of which are thought to be garnets. The red family member almandine was a very popular gemstone with the [[Germanic jewelry|Germanic tribes]] which inhabited northern Europe during Roman times. They were used for [[cloisonné]] inlay work of which the items found at Sutton Hoo are a great example.
  
 
[[File:Sut hoo2.jpg|center|500px]]
 
[[File:Sut hoo2.jpg|center|500px]]

Revision as of 18:08, 2 January 2013

Meet the family

Admired by mankind as long as history can take us back and available in many colors, garnets have been an important gem material throughout times. Both historical and archaeological research dates the use of garnets as a gem material back to the earliest known civilisations.

Pomegranate seeds, the fruit garnet may derive its name from
The family has possibly gained its name after the red varieties which resemble the seeds of a pomegranate in color. The term garnet now stands for a whole family of minerals that crystallizes in the cubic system and shares the same chemical blueprint. The elements used to fill that blueprint make a gem garnet belong to one or more of the following family members:
  • Pyrope: Mg3Al2(SO4)3 (magnesium aluminum silicate)
  • Almandine: Fe3Al2(SiO4)3 (iron aluminum silicate)
  • Spessartine: Mn3Al2 (SiO4)3 (manganese aluminium silicate)
  • Grossular: Ca3Al2(SiO4)3 (calcium aluminum silicate)
  • Hydrogrossular: Ca3Al2(SiO4)3-x(OH)4x (calcium aluminum silicate with hydroxide)
  • Andradite: Ca3Fe2(SiO4)3 (calcium iron silicate)

Garnet names

It would have been easy if nature presented us with pure family members but unfortunately for those trying to classify garnets, this isn't the case. The family members that are listed above represent end members within the garnet group. In other words their composition is an ideal, theoretical one. In reality all the garnets we use as gem materials are a mix of two or more end members in various ratios. Some of the magnesium which makes a pyrope a pyrope can be replaced by iron, or some of the iron that makes an almandine an almandine is replaced by manganese. In gemology this 'mixing of end members' is called isomorphous replacement. The composition of a garnet determines certain measurable characteristics of the stone such as refractive index and specific gravity. It can also influence the color of the stone which is why garnets come in many colors and shades. The confusion which occurs from these mixed garnets together with marketing strategies have caused an array of trade names to be invented for various garnets. While it is scientifically correct to call the the green garnet found in Kenya a green grossular, you will never encounter it under any other name than Tsavorite. It just sells better that way. Some names are relatively new and are still being contested, others have been in use so long that they have gotten a firm grounding in literature and have been adopted by gemologists. It is important to remember that at the end of the day all garnets are a mix of two or more of the end members mentioned above.

Garnet names
Rhodolite Anthill
Malaya Hessonite
Tsavorite Demantoid
Mandarin Topazolite
Mali Melanite

Below follows a diagram of trade names placed into context by their actual composition put together by dr. W. Wm. Hanneman:

© W. Hanneman, used with permission

Garnets in history

Garnets have been used wherever they occur for as long as mankind can remember. From predynastic Egypt to the discovery and hype of Fanta orange garnets in Tanzania in 2007, garnets have never ceased to capture our attention. The Roman writer Pliny mentions gemstones called carbuncles, some of which are thought to be garnets. The red family member almandine was a very popular gemstone with the Germanic tribes which inhabited northern Europe during Roman times. They were used for cloisonné inlay work of which the items found at Sutton Hoo are a great example.

Sut hoo2.jpg

In Victorian times garnets were extremely fashionable; rose cut garnets from the Czech Republic covered entire jewelry items. These garnets are better known as Bohemian garnets after the area they were mined: Bohemia.

Bohemian.jpg

In 1853 andradite was found in the Ural Mountains in Russia. This bright green garnet was named demantoid in 1878 and became a hot gemstone in 'turn of the century' jewelry. In the last quarter of the 20th century various garnet varieties have been found in Africa which enjoy a great popularity to this day.

Gemological properties

Gemological information for garnet
Color all colors
Crystal Structure Cubic
Refractive Index 1.74-1.89
Durability Good
Hardness 6.6-7.5
Treatments Usually not treated
Country of origin Worldwide
Garnet care
Ultrasonic cleaning Safe
Steam cleaning Safe
Warm soapy water Safe
Chemical attack Avoid
Light sensitivity Stable
Heat sensitivity Stable

Online G&G articles on garnet

Lang Antiques
Lang Antiques