Almandine
Almandine is the iron-rich end member of the garnet group, with the formula Fe3Al2(SiO4)3, and it is the most common garnet found in metamorphic rocks. It typically forms deep red to brownish-red crystals in mica schists and gneisses, distinguished by its density and classic dodecahedral crystal form. Almandine is the garnet most often cut for inexpensive faceted gemstones sold as "garnet" in jewelry.
Almandine properties at a glance
| Type | Minerals |
|---|---|
| Chemical formula | Fe3Al2(SiO4)3 |
| Mohs hardness | 7–7.5 |
| Crystal system | Cubic |
| Luster | Vitreous to resinous |
| Streak | White |
| Cleavage | None (indistinct parting) |
| Fracture | Conchoidal to uneven |
| Specific gravity | 3.9–4.3 |
| Transparency | Transparent to translucent |
| Common colors | Deep red, Reddish brown, Purplish red, Black |
| Rarity | common |
Geology & background
Almandine forms primarily during regional metamorphism of aluminum-rich sedimentary rocks, growing as porphyroblasts in schist and gneiss as temperature and pressure increase during mountain-building events. Classic localities include the garnet schists of India, Idaho's Emerald Creek (famous for star garnets), the Adirondacks of New York, and Alaska, where beach sands near Wrangell yield loose crystals. It also occurs as a detrital mineral in stream sediments and beach sands because of its hardness and resistance to weathering.
Collectors prize well-formed almandine crystals showing sharp trapezohedral or rhombic dodecahedral faces embedded in a schist matrix, and rare Idaho and India material can display four- or six-rayed asterism when cut as cabochons. Because almandine is common and generally inexpensive, it is an accessible mineral for building a reference suite of garnet species. Specimens with intact crystal faces and minimal fracturing command more interest than broken or included material, and matrix pieces showing the host schist add scientific value.
How to identify Almandine
Almandine typically appears deep red to reddish-brown or nearly black, with a vitreous to slightly resinous luster and a white streak despite its dark body color. It has a hardness of about 7 to 7.5, no true cleavage but conchoidal to uneven fracture, and commonly forms rounded rhombic dodecahedra or trapezohedra in schist. It is denser than most look-alike red minerals, which helps separate it from spinel, ruby, or andradite garnet; the lack of cleavage and rounded crystal shape distinguish it from staurolite.
- Compare the specimen's color, luster, crystal habit, grain size, streak, and locality before confirming.
- Use multiple photos when possible, including a fresh surface and a close view of texture.
Where Almandine is found
Reported from multiple localities worldwide; verify locality against specimen provenance when available.
How much is Almandine worth?
| Entry-level specimen | $2 |
|---|---|
| Typical collector specimen | $20 |
| Premium specimen | $150+ |
Value depends on size, crystal quality, color, locality, rarity, damage, and provenance.
Common uses
- Collector specimens
- Education
- Field identification
- Industrial or lapidary use when suitable
Interesting facts
- Idaho's Emerald Creek and Star Garnet Locality is one of only two places in the world where gem-quality star garnets are mined.
- The name garnet derives from the Latin granatus, referring to the resemblance of garnet crystals to pomegranate seeds.
- Almandine forms a continuous solid-solution series with pyrope garnet, so many natural garnets are chemical blends of the two.
Care & safety
Handle as a collector specimen until hardness, cleavage, and fracture are verified.
Avoid inhaling dust. Do not cut, grind, or polish unknown specimens without eye protection and a proper respirator.
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