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Almandine Garnet

 

Almandine (variety of Garnet)

 

Discovered in Prehistory; IMA status: Valid (pre-IMA; Grandfathered)

 

Chemistry

 

 

Chemical Formula:

Fe2+3Al2(SiO4)3

 

Iron Aluminum Silicate

Molecular Weight:

497.75 gm

Composition:

Aluminum

10.84 %

Al

20.48 %

Al2O3

 

Iron

33.66 %

Fe

43.30 %

FeO

 

Silicon

16.93 %

Si

36.21 %

SiO2

 

Oxygen

38.57 %

O

 

 

 

 

100.00 %

 

100.00 %

= TOTAL OXIDE

 

 

Classification

   

   

Mineral Classification:

Silicates (Germanates)

Strunz 8th Ed. ID:

8/A.08-20

Nickel-Strunz 10th Ed. ID:

9.AD.25

 

9 : SILICATES (Germanates)
A : Nesosilicates
D : Nesosilicates without additional anions; cations in [6] and/or greater coordination

Related to:

Garnet Group. Almandine-Pyrope Series. Almandine-Spessartine Series. Pyrope-Grossular Series.

Members of Group:

Garnet Group: Almandine, Andradite, Grossular, Pyrope, Spessartine, Uvarovite

Varieties:

Dhanrasite, Star Garnet

Synonyms:

Adelaide-rubin, Adelaide ruby, Alabandine Ruby, Alamandine, Almandine Garnet, Almandite, Oriental Garnet

 

 

Crystal Data

   

   

Crystallography:

Isometric - Hexoctahedral

Crystal Habit:

Typically well-formed dodecahedra or trapezohedra, to 1 m; also in rounded grains and massive.

Twinning:

None

 

 

Physical Properties

   

 

Cleavage:

Parting on {110}

Fracture:

Subconchoidal

Tenacity:

Brittle

Moh's Hardness:

7.0 - 7.5

Density:

4.318 (g/cm3)

Luminescence:

None

Radioactivity:

Not Radioactive

 

 

Optical Properties

   

   

Color:

Deep red, brownish red, red-violet, black; may be sectored.

Transparency:

Transparent to Translucent

Luster:

Vitreous to Resinous

Refractive Index:

1.830 Isotropic

Birefringence:

0.000 (Isotropic)

Dispersion:

Weak

Pleochroism:

None

 

 

Occurances

   

   

Geological Setting:

The most common garnet, typically in mica schists and gneisses, from regionally metamorphosed argillaceous sediments and pelites; also in contact metamorphic hornfels. In granites and eclogites; in sedimentary rocks; as a detrital mineral.

Common Associations:

Biotite, Cordierite, Chlorite, Staurolite, Andalusite, Kyanite, Sillimanite, Hematite, Plagioclase, Amphibole, Pyroxene

Common Impurities:

None

Type Locality:

Alabanda, Aydin Province, Aegean Region, Turkey

Year Discovered:

Prehistory

View mineral photos:

Almandine Mineral Photos and Locations

 

 

More Information

   

   

 

Mindat.org
Webmineral.com

 

 

Almandine is a member of the Garnet Group of minerals that includes Almandine, Andradite, Grossular, Pyrope, Spessartine and Uvarovite. Almandine is the most common variety of Garnet. Almandine always contain some Spessartine and Pyrope components which creates a wide range of colors including brown, red-brown, purplish red, wine red, purple and deep red. Almandine is the iron aluminum garnet. Pure Almandine and pure Pyrope are rare in nature and most specimens are a percentage of the two. Silky inclusions may be present in many Almandine gems that is only visible under magnification. However, material from Idaho, USA and India is known to contain inclusions of asbestiform minerals such as pyroxene and amphibole which create a chatoyancy that produces a 4-rayed star.

Almandine, like other varieties of Garnet, forms rounded crystals with 12 rhombic or 24 trapezoidal faces or combinations of these and some other forms. This crystal habit is classic for the Garnet Group of minerals.

Almandine was named for Alabanda in Turkey, an ancient gem cutting center.

Distribution: Widespread. Some localities for fine crystals include: in the Zillertal, Tirol, Austria. At Falun, Sweden. In Norway, from near Bod¿. From the Akhmatovsk deposit, near Zlatoust, Ural Mountains, Russia. In the USA, from Roxbury, Litchfield County, and Southbury, New Haven County, Connecticut; at Auburn, Androscoggin County, and Topsham, Sagadahoc County, Maine; from Westfield and Russell, Hampden County, Massachusetts; and at Hanover, Grafton County, New Hampshire. From Avondale, Chester County, Pennsylvania; a large commercial deposit at the Barton mine, North Creek, Warren County, New York; at Michigamme, Marquette County, Michigan; from Salida, Chaffee County, Colorado; and at Ft. Wrangell, Stikine River, Alaska. In Brazil, at Pernambuco, Bahia. From the Miami district, Zimbabwe. At Broken Hill and Thackaringa, New South Wales, and in the Harts Range, Northern Territory, Australia. From Yamanoo, Ibaragi Prefecture, and the Ishikawa district, Fukushima Prefecture, Japan.

Almandine gems for sale:

We have not photographed our Almandine gems yet. Please check back soon.

 

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