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Almandine
Almandine is the ferrous iron end member of the class of garnet minerals from the isomorphous subgroup of piralspit group of garnets, colored in red with light orange, brownish or purple hues or without them. The name is a corruption of Alabanda area (now the Aydin province in Turkey), a region in Asia Minor, where this mineral and other "carbuncles" predominantly entered the markets of ancient Europe from (according to Pliny the Elder). The name of the mineral was introduced into use in 1546 by Georgius Agricola, the real name is Georg Bauer, years of life 1494-1555, in the work "Bermannus sive de re Metallica" (On Mining and Metallurgy).
Chemistry: Fe3Al2(SiO4)3;
Crystal system: Cubic, hexoctahedral crystal class (point symmetry group);
Color: Red, reddish orange to red, slightly purplish red to reddish purple and usually dark in tone.
The red color in almandine is due mainly to the chromophore center of Fe82+, an isomorphous impurity of Mn2+ can be presented as an additional chromophore. Additionally, the isomorphous admixtures of Ca2+ and Mg2+ influence the coloring, somewhat fading it.
Identification properties
| Physical properties | |
|---|---|
| Mohs hardness: | 7-7,5 |
| Density: | from 3,93 to 4,17 (calculated 4,298) g/cm3 |
| Cleavage: | none or imperfect on (110) |
| Fracture: | conchoidal |
| Optical properties | |
|---|---|
| Optical character: | isotropic, sometimes anomalous anisotropic |
| Refractive Index: | 1,770 – 1,820 (calculated 1,827 – 1,830) |
| Birefringence: | none; anomalous – to 0,005 |
| Pleochroism: | none |
| Dispertion: | 0,024 (BG) |
| Luster: | vitreous |
Inclusions and structural inhomogeneities
Gem basic treatments
| Treatment | Goal |
|---|---|
| Impregnation with high refractive glasses (for large stones) to fill the open cavities | Improving the gem properties |
Synthetic or Imitation gem materials
Synthetic garnet-almandines for the jewelry industry are not produced.
The most commonly encountered synthetic almandine is as follows:
- synthetic garnet minerals;
- synthetic spinels;
- doublet: garnet + glass;
- color glass.
