Short review about Garnet and Photos of  Garnet specimens from my private collection :


        The garnets are a group of mineral species all having essentially the same isometric crystal structure but varying in chemical composition and in many of their physical properties.
         There are six species of common garnets based on ideal end-member chemical compositions. These six species are divided into two groups; the pyralspite group which are the pure chemical end-members Fe3Al2(SiO4)3 (almandine), Mg3Al2(SiO4)3 (pyrope) and Mn3Al2(SiO4)3 (spessartine), and the ugrandite group or calcium garnet group consisting of Ca3Fe2(SiO4)3 (andradite), Ca3Al2(SiO4)3 (grossular), and Ca3Cr2(SiO4)3 (uvarovite, which actually is not 'common' at all!). Extensive solid solution occurs within these two groups, but normally very little substitution occurs between them.
Garnets very rarely if ever occur in nature with compositions precisely matching the pure end-member common garnet species (almandine, pyrope, spessartine, andradite, grossular and uvarovite). A natural garnet's composition typically falls somewhere between these end-members, somewhere within the solid solution ranges for the pyralspite group or the ugrandite group. Varietal names have been given to some garnets of intermediate composition in these solid solution series such as the rose-red to purple rhodolite garnet, which has a chemical composition averaging a 2:1 mixture of pyrope to almandine. An additional intermediate variety between pyrope and almandine with a chemical composition averaging a 1:1 mixture of pyrope to almandine is the Mozambique garnet with its beautiful dark orange-red to red color. Another intermediate composition example is the yellow to orange to red garnet variety malaia which is of an intermediate composition range between spessartine and pyrope. This garnet variety also has a significant grossular component, which is quite unusual and unexpected due to the significant size difference between the substituting ions.
The ions Cr3+, V3+ and Ti3+/4+ can substitute in some of the common garnet compositions or occur as trace impurities, resulting in numerous less common garnet varieties. Some of these less common garnet varieties are of specific colors such as the green vanadium grossular garnet variety tsavorite and the green chromium andradite garnet variety demantoid. When significant amounts of vanadium and chromium impurities occur in malaia garnets, a distinct color change is visible when viewed under fluorescent light versus incandescent light. Garnets exhibiting this rare color beavior are known as color change garnets.
Grossular garnets of yellow-orange to orange-red to brown colors are known as hessonite garnets. Some grossular garnet occurs in a translucent massive form known as hydrogrossular with (OH)4-4 substituting for (SiO4)-4 tetrahedra in its crystal structure.
Garnet is allochromatic, meaning that most of the color variations in different garnets are due to their highly variable trace element impurities rather than to their bulk composition elements. The color we see in garnets is produced when light is selectively absorbed by these ions or by interactions between these ions (intervalent charge transfers).
It is not possible to determine the precise species or variety of a garnet based solely upon a comparison of its refractive index and specific gravity (let alone determining a variety solely by its color!), although comparing the refractive index and specific gravity can narrow down the possibilities considerably.
In most cases, unit cell dimension measurements can be compared with the refractive index and specific gravity to determine chemical composition in terms of major end-members. In the absence of chemical analysis some ambiguitiy will often still exist, leaving one to rely on additional information such as occurance, associated minerals and color.
However, methods that rely on specific gravity measurement can be misleading, because the specific gravity is not only difficult to measure accurately, but also is prone to error in garnets due to their abundant inclusions which can alter their specific gravity considerably.
Perhaps the most reliable method outside of chemical analysis for determining garnet species and varieties in gem garnets is by comparing their absorption spectrum, refractive index and color, which gives a conclusive identification.
Some almandine garnets form with asbestiform mineral inclusions, typically of pyroxene or amphibole, that give a chatoyant effect yielding a four-ray star when fashioned into a cabochon gem.

       Garnets form in a variety of geologic settings, depending on the garnet species.
Almandine typically occurs in schists and gneisses, resulting from regional metamorphism of argillaceous sediments. It is a characteristic mineral constituent of the amphibolite metamorphic facies, also appearing in the granulite facies. Almandine also occurs in pegmatite dikes and in some granitic and volcanic rocks, as well as in sedimentary deposits as detrital grains.
Pyrope is characteristic of ultra-mafic rocks such as peridotites, kimberlites, eclogites, and serpentines, and in sedimentary deposits derived from their weathering.
Spessartine occurs occaisionally in granitic pegmaties and in skarns, also found in sedimentary deposits.
Andradite commonly occurs in contact metamorphic deposits, resulting from metamorphism of impure limestones. It also is found in some metasomatic skarn deposits. The light colored andradite varieties topazolite and demantoid occur mainly in serpentinites and chlorite schists. The darker andradite varieties melanite and schorlomite occur mainly in alkaline igneous rocks such as nepheline syenites and phonolites.
Grossular occurs mainly in contact and regional metamorphic deposits, resulting from metamorphism of impure limestones. It also has been found in alkaline igneous rocks, and has been reported in pegmatites and hydrothermal veins.
Uvarovite is a rare garnet occurring in peridotite and serpentinite associated with chromite.
Garnets are usually recognized by their form, color and hardness. The garnet varieties can be distinguished by their refractive index, absorption spectrum and color. Another method utilizes specific gravity, refractive index and unit cell dimension.

       The name garnet is from the Latin word granatus which originated when garnet grains in rock were compared to the dark red seeds of the pomegranate fruit.
Pyralspite is derived from the names of the three garnet species in its group: PYRope, ALmandine, and SPessartine, with 'ite' added to the end.
Ugrandite is derived from the names of the three garnet species in its group: Uvarovite, GRossular, and ANDradite, with 'ite' added to the end.
Almandine was named after the ancient locality Alabander in Asia minor, where once many garnets were cut and polished.
Pyrope is from the Greek for fire-like, refering to its color.
Spessartine was named for a locality in the Spessart district in Bavaria.
Andradite was named after the Portuguese mineralogist d'Andrade.
Grossular was named after the gooseberry R. grossularia, because of the similar pale green color of the original specimens.
Uvarovite is named after the Russian mineralogist Count Sergei Simonovitch Uvarov.
Rhodolite is from the Greek rhodon meaning rose, refering to its color.
Malaia is from the Swahili word malia meaning out of the family, refering to the fact that this garnet variety typically has some distinctively different physical properties than other garnets found in the same area.
Tsavorite is named after the Tsavor Game Preserve of Kenya, near which it was discovered.
Demantoid is from the French demant meaning diamond, in allusion to its similar brilliance.
Melanite is from the Greek melanos meaning black, refering to its color.
Topazolite named after its similarity to yellow topaz.

     Garnets have been used as gemstones for many thousands of years. In ancient times they were known as carbuncles, as were other red gems. They were in the 'Breastplate of Judgement' of Aaron, described in the bible (Exodus: xxviii, 15-30). The Koran states that the fourth heaven is composed of carbuncle. In Vedic astrology ( 1000's of years older than western astrology and still practiced by millions today), the brownish-orange/red hessonite garnet has long been a preferred talisman for warding off the evil influences of the celestial body named Rahu. Garnet was considered a sacred stone by many native indian tribes of North, South and Central America.
In 1892, the Hunzas used bullets made of garnet against the British troops in Kashmir, believing them to be more deadly than lead.
Historically, garnets were believed to give protection from wounds and poison, to stop bleeding and to symbolize truth & fidelity, and bring prosperity.
     As gemstones, garnets today are more popular than ever. Some of the newer varieties have only become available in recent years.
Garnets are also used today for a number of abrasive purposes.

 

Garnets from Russia :


uvarovite garnet

Uvarovite, Saranovskii Mine , Saranovskaya Village, Gorozavod area, Permskaya Oblast', Middle Urals, Urals Region, Russia

Spc. Num.  G-002

Size 75 x 60 x 35 mm

(single crystals up to 7mm !)

andradite garnet

Interesting specimen, where two generation andradite garnet crystals on matrix rock we can see, from rare locality - Dashkesan Co-Fe deposit, Azerbaijan

Spc. Num.  G-041

Size 112 x 80 x 35 mm

grossular garnet

XL crystal of green grossularite, from Vilyui River, Saha Republic, Yakutia, Eastern-Siberian Region, Russia  (Ex. Mr. Vladimir Chernavcev collection)

Spc. Num.  G-012

Size 47 x 36 x 35 mm 

уваровит андрадит гроссуляр

grossular garnet

Grossular (Var. Hessonite) Bajenovskoe dep., Asbest, Ural, Russia

Spc. Num.  G-026

Size 80 x 60 x 42 mm

grossular garnet

Large specimen of Grossular (Var. Hessonite) garnet, from Bajenovskoe dep., Asbest, Ural, Russia

Spc. Num.  G-005

Size 130 x 85 x 100 mm

andradite garnet

Perfect specimen of green colored Andradite garnet, that was collected many years ago at well known locality - Sinerechenskoe skarn occurrence, Kavalerovo Mining District, Dalnegorsk, Primorskiy Kray, Far-Eastern Region, Russia

Spc. Num.  G-009

Size 85 x 62 x 57 mm

гессонит гроссуляр  

Garnets from Africa :


Tsavorite garnet

Tsavorite garnet, Merelani Hills (Mererani), Lelatema Mts, Arusha Region, Tanzania

Spc. Num.  G-020

Size 40 x 38 x 28 mm  

spessartine garnet

Perfect quality, XL Spessartine crystal, from Nani, Loliondo, Arusha Region, Tanzania

Spc. Num.  G-017

Size 77 x 78 x 67 mm

spessartine garnet

Perfect quality, XL spessartine crystals cluster, from Nani, Loliondo, Arusha Region, Tanzania

Spc. Num.  G-018

Size 85 x 75 x 55 mm

цаворит спессартин спессартин
andradite garnet

Very aesthetic, large, melanite garnet cluster (crystals size up to 35mm), from Diakon, Nioro du Sahel Circle, Kayes Region, Mali

Spc. Num.  G-023

Size 100 x 78 x 50 mm

topazolite garnet

Gemmy quality, with XL crystals on matrix rock, topazolite specimen, from Antetezambato (Tetezambato), Ambanja, Ambanja District, Diana Region (Northern Region), Antsiranana Province, Madagascar

Spc. Num.  G-008

Size 65 х 48 х 32 mm

demantoid garnet

Gemmy quality, demantoid crystals on matrix rock, from Ambanja District, Diana (Northern) Region, Antsiranana Province, Madagascar

Spc. Num.  G-028

Size 95 x 75 x 35 mm

  андрадит  
demantoid garnet

Demantoid, Tubussis 22 farm (Tubussis; Tubusis; Tubessis), Karibib District, Erongo Region, Namibia

Spc. Num.  G-022

Size 79 x 65 x 70 mm

   
топазолит    

Garnets from China :


spessartine garnet

Spessartine, Wushan Spessartine Mine, Tongbei, Yunxiao Co., Zhangzhou Prefecture, Fujian Province, China

Spc. Num.  G-010

Size 100 x 70 x 60 mm

spessartine garnet

Hight quality, bright Spessartine garnet specimen, from Wushan Spessartine Mine, Tongbei, Yunxiao Co., Zhangzhou Prefecture, Fujian Province, China

Spc. Num.  G-036

Size 107 x 80 x 36 mm

spessartine garnet

Spessartine, Wushan Spessartine Mine, Tongbei, Yunxiao Co., Zhangzhou Prefecture, Fujian Province, China

Spc. Num.  G-011

Size 210 x 65 x 64 mm

  спессартин  

Garnets from Other Asian countries :


demantoid garnet

Single, XL demantoid crystal, from Soghan, Baft District, Kerman Province, Iran

Spc. Num.  G-007

Size 32 x 32 x 31 mm

demantoid garnet

Demantoid, Ghazni (Gazni) Province, Afghanistan

Spc. Num.  G-016

Size 106 x 60 x 45 mm

Melanite ( Andradite ) garnet

Melanite (Andradite), Sokol'noye Iron Mine, Rudnyi Altai, Qostanay Oblast', Kazakhstan

Spc. Num.  G-003

Size 95 x 64 x 39 mm

демантоид демантоид меланит

Garnet Hessonite

Garnet Hessonite, Gilgit, Gilgit District, Northern Areas, Pakistan

Spc. Num.  G-001

Size 60 x 47 x 45 mm

Garnet Hessonite

Garnet Hessonite, from Mana Mine, Barang, Bajawar, Federally Administered Tribal Areas, Pakistan

Spc. Num.  G-030

Size 80 x 60 x 32 mm

spessartine garnet

Large spessartine garnet crystal, that sitting on quartz, from Shigar Valley, Skardu District, Baltistan, Northern Areas, Pakistan

Spc. Num.  G-032

Size 36 x 28 x 27 mm

спессартин гессонит спессартин

Garnet Hessonite

Garnet Hessonite, from Mana Mine, Barang, Bajawar, Federally Administered Tribal Areas, Pakistan

Spc. Num.  G-004

Size 36 x 32 x 20 mm

   
     

Garnets from European countries :


Demantoid garnet

Demantoid, Malenco Valley, Sondrio Province, Lombardy, Italy

Spc. Num.  G-013

Size 70 x 45 x 20 mm

uvarovite garnet

Outstanding, uvarovite specimen, from Outokumpu Cu-Zn deposit, Outokumpu Cu-Co-Zn-Ni-Ag-Au ore field, Eastern Finland Region, Finland

Spc. Num.  G-006

Size 107 x 42 x 36 mm

 
демантоид    

Garnets from Sourth and North America:


 spessartine garnet

Etched spessartine garnet crystal from Navegadora Mine, Penha do Norte, Conselheiro Pena, Doce valley, Minas Gerais, Southeast Region, Brazil

Spc. Num.  G-029

Size 80 x 50 x 45 mm

Grossular garnet

Grossular garnet specimen, from Jeffrey Mine (Jeffrey Quarry), Asbestos, Shipton Township, Richmond Co., Québec, Canada

Spc. Num.  G-015

Size 80 x 70 x 16 mm 

Topazolite garnet

Topazolite, Jeffrey Mine (Jeffrey Quarry), Asbestos, Shipton Township, Richmond Co., Québec, Canada

Spc. Num.  G-019

Size 65 x 35 x 23 mm

гранат, коллекционные минералы, гроссуляр, гессонит, спессартин, уваровит, андрадит, цаворит, кристаллы, меланит, демантоид

© Oleg Lopatkin