Garnet

Garnets are a set of closely related minerals which occur in many colours – not just reds or dark reds. Well known members of the Garnet group include Almandine, Grossular, Hessonite, Pyrope, Spessartine.. don’t worry, there’s more.

Garnets can occur in reds, pinks, greens, oranges, and rarely, blue. They are most often used for jewellery or industry.

Uses and History

Garnets are a group of silicate minerals – not just the red Garnet most people know of!

Garnets have been used as gemstones since the Bronze Age and were some of the most commonly used gemstones in the Roman world, as well as Anglo-Saxon England – using an inlay technique called ‘cloisonne’.

The archaeological evidence produced by these finds gives us a wealth of evidence about early civilisations – we can determine that there were trade routes from the UK and Europe stretching as far as Sri Lanka and India.

Garnet is also used as an abrasive, due to its relatively high hardness – often used for a media in sand blasting and water jet cutting.

Mineralogy, colours, and variants

Almandine

Andradite

Demantoid

Chemistry
An Iron aluminium silicate. Fe3Al2Si3O12
Ca3Fe3+2Si3O12
Ca3Fe2Si3O12
Colours and Variations
Dark red, red, ‘rusty’, black, reddish brown, black with red edges or hints.
Red, green, yellow, orange, multicoloured, brown, pink, grey, black.
Green gemstone variety of Andradite Garnet.
Streak
Colourless.
White.
Colourless.
Luster
Vitreous
Adamantine, submetallic
Adamantine
Fracture
Conchoidal to uneven
Conchoidal to uneven
Conchoidal to uneven
Crystal habit
Dodecahedral and trapezohedral crystals, often striated or with stepped growth layers. Almandine also occurs in grainy and massive forms, depending on locale.
Dodecahedral and trapezohedral crystals, as well as granular and massive specimens depending on locale.
Cubic
Mohs hardness
7.5 – 8.5
6.5 – 7.5
6.5 – 7.0
Specific Gravity
4.3
3.8 – 3.9
3.84
Locales
Common worldwide, with gem grade specimens found in India, Sri Lanka, Madagascar, Brazil, Australia
Russia, Namibia, Afghanistan, Italy, Madagascar.
Russia, Namibia, Afghanistan

 

Grossular

Hessonite

Hydrogrossular

Chemistry
Ca3Al2Si3O12
Transparent gemmy variety of Grossular Garnet.
Calcium Aluminium Garnet with hydroxide partially replacing silica.
Colours and Variations
Pure Grossular is colourless.
Impurities and inclusions cause various colours:
red, green, white, grey, black, yellow, orange, purple.
Orange to orange brown.
green to blue green, pink, white, grey
Streak
Brown
Luster
Greasy, Vitreous to Adamantine
Vitreous to resinous
Vitreous
Fracture
Conchoidal to uneven
Conchoidal
Conchoidal
Crystal habit
Massive
Mohs hardness
6.5 – 7.5
6.5 – 7.0
7.0 – 7.5
Specific Gravity
3.5 – 3.65
3.40 – 3.71
4.12 – 4.20
Locales
Kenya, Tanzania, Mali, Italy, Russia, Mexico, Canada, USA
Canada, Afghanistan, Italy, Sri Lanka, Tanzania, India
Burma, Canada, China, South Africa, USA

 

Malaya

Mandarin

Melanite

Chemistry
Spessartine Garnet – (Mg,Mn)3Al2(SiO4)3
Bright orange Spessartine Garnet.
Black / dark red Andradite Garnet – Ca3Fe3+2(SiO4)3
Colours and Variations
Pinkish Red, orange
Orange, yellow orange, reddish orange.
Black, very dark red
Streak
Luster
Vitreous to adamantine
Vitreous
Sub-adamantine to vitreous.
Fracture
Conchoidal
Conchoidal
Crystal habit
Isometric, dodecahedral, trapezohedral
Mohs hardness
7 – 7.5
7 – 7.5
6.5 – 7.0
Specific Gravity
3.78 – 3.85
4.05 – 4.20
3.71 – 4.10
Locales
East Africa, Tanzania, Kenya.
Tanzania, Namibia, Nigeria.
Russia, USA, Mali, Mexico, France, Italy.

 

Pyrope

Rhodolite

Spessartine

Chemistry
Mg3Al2Si3O12
(Mg,Fe)3Al2Si3O12
Mn3Al2Si3O12
Colours and Variations
Red, mostly dark, almost black.
Red, purple
Red, Yellow, Orange, Brown, Pink
Streak
White
White
White
Luster
Vitreous
Vitreous
Adamantine
Fracture
Conchoidal
Conchoidal
Sub-conchoidal
Crystal habit
Typically rhombic dodecahedral.
Typically rhombic dodecahedral.
Massive to crystalline.
Mohs hardness
7 – 7.5
6.5 – 7.5
7
Specific Gravity
3.5 – 3.8
3.9 – 4.3
4.1 – 4.2
Locales
Australia, Austria, Brazil, Czech Republic, Italy, South Africa, Tanzania, USA
Brazil, Sri Lanka, Myanmar, Tanzania, USA, Mozambique.
Afghanistan, Brazil, Canada, China, France, Germany, Italy, Madagascar, Mexico, Namibia, Nigeria, Pakistan, Portugal, Russia, South Africa, Spain, Tanzania, USA.

 

Topazolite

Tsavorite

Uvarovite

Chemistry
Ca3Fe3+2(SiO4)3
Ca3Al2Si3O12
Ca3Cr2Si3O12
Colours and Variations
Lemon-yellow to yellow-brown.
Green, given its colour by Chromium or Vanadium.
Green, given its colour by Chromium.
Streak
White
White
Luster
Subadamantine, vitreous.
Vitreous to adamantine
Vitreous
Fracture
Conchoidal
Conchoidal, uneven
Uneven, conchoidal
Crystal habit
Dodecahedral, trapezohedral
Hexoctahedral
Mohs hardness
6.5 – 7.0
7.0 – 7.5
6.5 – 7.5
Specific Gravity
3.7 – 4.1
3.6
3.77 – 3.81
Locales
Germany, Iran, Italy, Madagascar, Mexico, USA
Kenya, Tanzania, Madagascar.
Afghanistan, Cuba, Finland, Russia, USA

 

Hazards and Warnings

Almost all rocks, minerals (and, frankly, almost all other substances on earth) can produce toxic dust when cutting, which can cause serious respiratory conditions including silicosis.

When cutting or polishing rocks, minerals, shells, etc, all work should be done wet to minimise the dust, and a suitable respirator or extraction system should be used.

Translations

Apologies for any mistranslations here – it turns out ‘garnet’ is very close to ‘grenade’ in some languages.

Arabic:

Hindi:

  • गारनेट के

Portuguese:

Bengali:

  • তামড়ি

Indonesian:

  • batu delima

Punjabi:

  • ਗਾਰਨੇਟ

English:

Italian:

  • granato

Russian:

  • красный гранат

French:

  • grenat

Japanese:

  • ガーネット

Spanish:

  • granate

German:

  • Granat

Korean:

  • 석류석
  • 가넷색

Thai:

  • โกเมน

Gujurati:

  • ગાર્નેટ

Mandarin and Traditional Chinese:

  • 石榴石

Urdu:

  • گارنیٹ

Further Reading / External Links