Grenades (silicates): Almandine

Diagnostic card.
On the picture. Crystals of almandine in shale rock (Jotzal, Austria).

Fe ₃ Al ₂ (SiO ₄ ) ₃
Cubic amount of cubic zirconia
Hardness 7-7,5
Specific weight 4,3
Cleavage is absent
Cracked shell
Color violet-red, brown-red
Color in powder white
Shine from glass to resin

His name was given to the Almandin through the city in Asia Minor. To better reveal the color of the stone, when it is processed in the cabochon from the underside, a depression is made. Almandine with the effect of asterism is called a star grenade. The most significant deposits of jewelry almandine are known in Sri Lanka, India, Afghanistan, Brazil, Austria and the Czech Republic.

Crystals of almandine are rhombododecahedrons and tetragon-trioctahedra, both forms often combined, sometimes round. Coloring is violet-red and brownish-red, less often orangeish-red. Glitter is glass and resin. Almandin is the hardest of all pomegranates, it has no cleavage, medium fragility, fractured shell. Large or small well-formed crystals, grains and their aggregates, ellipsoidal nodules and solid masses with a shell-like structure. Etching is observed on the crystals in the form of triangles, the faces are sometimes slightly shaded; On the faces of almandine crystals from metamorphic schists and sedimentary rocks of the Carpathians and the Carpathian Mountains there are steps of growth.

Almandine with a small content of Ca and Mg was called calcium pyrimandine (calc-pyralmandine), with a small content of Mn - manganese almandine, manganalmandine (manganalmandine). There is a continuous isomorphic series from almandine to pyrope and from almandine to spessartine.

Pure almandines of the composition Fe3Al2 [SiO4] 3 are rare, most often there is a pyrope component, as well as impurities of ions Fe3 +, Ca2 +, Mn2 +, etc. The color of the almandine is primarily associated with Fe2 + ions, with a decrease in the concentration of which there is some attenuation of color Stone, reducing its density. The presence of Fe3 + and Mn2 + ions leads to the appearance of red and orange hues in the almandines.

Almandine is usually found in the form of well-formed crystals - rhombododecahedrons, trigonotroctahedra, often with shading on the faces. The size of crystals from fractions to several tens of centimeters, but crystals of jewelry quality are usually small - 5-6 mm. Larger crystals are rare. At the Smithsonian Institution in the United States, a star almandine is stored. Idaho (USA) with a mass of 174 ct.

Diagnostic signs.
Sometimes it is characterized by weak magnetic properties. Inside, there may be rutile needles, which cause the effect of asterism, which manifests itself in the form of the appearance of a light asterisk. Fused into a dark magnetic ball. Does not dissolve in acids.

Origin.
It is formed mainly in metamorphic shale rocks, in granite pegmatites, as well as in igneous rocks of basic composition. The deposits of almandine are confined primarily to alluvial, eluvial and, to a lesser extent, to coastal-marine placers associated with erosion of metamorphic rocks-crystalline schists and gneisses of the almandine-amphibolite facies, microcline muscovite-beryl pegmatites and effusives of medium and acidic composition.

Place of Birth.
The best known deposits of India and Sri Lanka. Other significant deposits of almandine are in Brazil, South America and Madagascar. The best almandines are famous for Sri Lanka. Good stones are supplied by India and Brazil. There are almandines in the USA (Alaska, Fort-Wrangell, the states of Colorado, South Dakota, Michigan, New York, Pennsylvania, Connecticut, Maine, California), Canada, Austria, Japan, Tanzania, Zambia and Madagascar. In the CIS almandines are known since the 18th century - on the Kola Peninsula, in Karelia, in the Southern Urals, in Eastern Siberia (along the Mama River). The largest deposits are the Kientelskoe (on the shores of Ladoga Lake) and Chupinskoye.

Use in jewelry.
Almandine is treated with facets in the form of a mixed cut or rosette, sometimes in the form of a cabochon; In the past they made a depression in the middle of the stone to reduce the color saturation.

Almandin in the quartz. Petrovsky district. Krivorozhye, Ukraine. Photo: © А.А. Evseev.

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