Almandine is the iron aluminum member of the garnet group and the most common gem garnet. It ranges from dark red to purplish red and brownish red, and it is the stone most people picture when they hear "garnet." Almandine has been cut and set since antiquity, most famously in the gold cloisonne jewelry of early medieval Europe.
What almandine is
Almandine's ideal formula is Fe3Al2(SiO4)3, with iron in the X site and aluminum in the Y site. It belongs to the pyralspite series of garnets, along with pyrope (magnesium) and spessartite (manganese). Pure almandine is rare. Most gem stones contain some pyrope or spessartite mixed in, and the exact blend changes their color and properties.
Almandine is cubic and singly refractive. It is one of the denser garnets, with a specific gravity of about 3.9 to 4.3, and its refractive index of about 1.76 to 1.83 is often over the limit of a standard gem refractometer for iron-rich stones. Hardness is 7 to 7.5, and it has no cleavage, so it holds up well in jewelry. Iron gives a characteristic absorption spectrum with three strong bands in the yellow, green and blue-green, which gemologists see in a hand spectroscope. The gemological instruments page explains how a spectroscope is used.
The name is usually traced to Alabanda, an ancient city in Asia Minor where, according to Pliny the Elder, garnets were cut and polished.
Color
Almandine's color comes from ferrous iron, which is part of its chemical formula. Typical stones are deep red with a brown or purple undertone. Because the color is dense, larger stones can look almost black. Cutters often keep almandine shallow, or cut it as a cabochon, to lighten its appearance.
The most valued almandine is a clear, medium-dark red to purplish red without brown. Brownish stones are cheaper and common in commercial jewelry. Almandine is almost never treated. The color in gemstones page covers why iron produces red in garnet.
Rhodolite: pyrope and almandine mixed
Rhodolite is a trade name for garnet in the pyrope-almandine series with a lighter, purplish red to raspberry or rose color. The name comes from the Greek for "rose stone." It was first used for garnets found in North Carolina in the late nineteenth century. Major later sources include East Africa (Tanzania and Kenya), Sri Lanka, India, Madagascar, Brazil and Mozambique.
Rhodolite is brighter and more transparent than typical almandine, so it can be faceted in larger sizes without looking dark. It is one of the more popular garnet varieties in modern jewelry. Like other pyralspites, it is rarely treated.
Gemologists separate pyrope, almandine and rhodolite by refractive index, specific gravity and spectrum, but for jewelry purposes the trade name usually follows color.
Star almandine
Some almandine contains fine rutile needles aligned along the crystal's directions. When cut as a cabochon, these needles reflect light into a star, usually with four rays and sometimes six. Star garnet has come from Idaho, where it is the state gem, and from India. The stones are usually dark and opaque to translucent, and the star shows best under a single light source. This kind of star effect is called asterism and is described on the gemstone optics page.
How almandine forms
Almandine forms mainly in metamorphic rocks such as mica schist and gneiss, where clay-rich sediments are buried, heated and squeezed. Its crystals often grow as well-formed dodecahedrons or trapezohedrons scattered through the rock. Geologists use almandine as an indicator of metamorphic grade. It also forms in some granites and pegmatites.
Because almandine is hard and dense, it survives weathering and concentrates in river and beach sands. Sri Lanka's gem gravels and India's river deposits have supplied it for thousands of years. Low-quality almandine is mined in bulk for garnet abrasive, used in sandpaper and waterjet cutting. The metamorphic rocks and gemstones page covers these settings.
Almandine in ancient and medieval jewelry
Garnets, many of them almandine, were among the most popular colored stones of the ancient world. Greek and Roman jewelers set them as cabochons and carved them as intaglios for seal rings. The ancient Roman jewelry page covers that tradition.
From the fourth to the seventh century, jewelers across Europe developed garnet cloisonne. They cut garnet into thin, flat plates shaped to fit small gold cells (cloisons), often with patterned gold foil underneath to reflect light back through the stone. The technique spread with the Goths, Franks, Lombards and Anglo-Saxons. The gold and garnet fittings from the Sutton Hoo ship burial in England, found in 1939, are among the best-known examples, and the Staffordshire Hoard found in 2009 held many more. Chemical studies of early medieval garnets point to India and Sri Lanka as sources for much of the material used before about 600 AD, which means the stones traveled thousands of kilometers. Read more on the medieval jewelry and cloisonne enamel pages.
Later, in the seventeenth to nineteenth centuries, almandine and pyrope were cut as rose cuts and table cuts for Georgian and Victorian jewelry.
Sources
Gem almandine and rhodolite come from India, Sri Lanka, Madagascar, Brazil, Tanzania, Kenya, Mozambique, Austria, the Czech Republic and the United States, among others. Almandine is common worldwide, but clean, attractive gem rough is less so. See gems of Sri Lanka for one historic source.
Identification and imitations
Almandine is easy to separate from most red gems with standard tests. It is singly refractive, unlike ruby, and denser than red spinel. Its iron spectrum is distinctive. Red glass and garnet-topped doublets have imitated it. Synthetic almandine is not a commercial product.
Wear and care
Almandine suits rings, earrings and pendants. It is hard enough for daily wear and has no cleavage. Clean it with warm soapy water and a soft brush. Ultrasonic cleaning is usually safe for clean stones; avoid it for stones with fractures. See the jewelry cleaning guide.
Frequently asked questions
What is the difference between almandine and pyrope?
Both are red garnets. Almandine is iron-rich and denser, often with a purplish or brownish tone. Pyrope is magnesium-rich and tends toward a purer red.
Is rhodolite a type of almandine?
Rhodolite is a pyrope-almandine blend with a lighter purplish red or rose color. It is usually treated as its own trade variety.
Is almandine garnet expensive?
Almandine is the most common gem garnet and is generally affordable. Clean stones with bright red color and star almandine with a sharp star are worth more.
Where does the name almandine come from?
The name is traced to Alabanda, an ancient city in Asia Minor where, according to Pliny the Elder, garnets were cut.