Garnet Group: Grossular Garnet (Tsavorite)
Grossular Garnet used in Jewelry
Source: Kenya, Madagascar, Tanzania, Siberia, USA
The mineral Grossular is a calcium-aluminium variety of the garnet group, who's name is derived from "grossularia," or "gooseberry," a fruit that closely resembles a pale-greenish grossular variety from Siberia, called viluite." Grossular is also known by the name "grossularite."
Grossularite Composition
Grossular is a calcium-aluminium nesosilicate with a granular, compact, and/or massive crystal growth habit, which forms rhombic dodecahedra or cubic crystals in the Isometric crystal system. Grossular's calcium component may be partially replaced by ferrous iron, and the aluminium component by ferric iron.
Grossular garnet occurs in a wide variety of colors from emerald green, to brown, olive green, orange, pink, and yellow. Color varieties of grossular include: Californite (American Jade), hessonite (cinnamon stone, Gomedhaka), hydrogrossular, Transvaal Jade, Viluites, and the highly prized Tsavorite.
Tsavorite
Tsavorite, also known by its European name "tsavolite," is an extremely rare variety of grossularite, that was first discovered near Komolo, in the Merelani Hills, approximately 50km southeast of Arusha, Tanzania. A British geologist named Campbell Bridges identified the first specimen of tsavorite in 1967.
Grossularite Metamorphic Matrix |
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Gemmy Tsavorite from Tanzania |
Tsavorite is a grossularite garnet with an intense emerald-green, grass-green, or bluish-green hue (photo: above, right) that is a combination of calcium and aluminum, containing trace amounts of chromium (Cr) and vanadium (V) as allochromatic coloring agents.
The primary source for Tsavorite is located in bush-country of south-eastern Kenya and in north-eastern Tanzania at the Komolo tsavorite deposit (aka "Lemshuko Tsavorite Mine") at Komolo, near Arusha, Tanzania (photos below).
Tsavorite occurs in two distinct geological settings, a primary or "hard rock" deposit, and as redeposited material found in secondary alluvial sands and gravels. In the decades since the tsavorite's discovery, local miners have blasted the hard rock and dug pits in the sand and gravel deposits, and have even attempted some tunneling in places where the garnet-rich gravel was sufficiently consolidated [1].
According to Eric Saul at Swala Gem Traders: "Tiny tsavorites are not rare, but stones sufficiently large to be the center stone in a ring are not easy to come by. We believe that this is because the incorporation of traces chromium and vanadium, which act as coloring-agents, affects the crystal lattice in ways that make it difficult for individual crystals to grow past a certain size. In consequence, large tsavorites are much rarer than large emeralds."
The name Tsavorite was coined by Tiffany & Company's president, Henry Platt in 1974; named for Tsavorite's discovery in the Tsavo National Park, Kenya. Tsavorite is reminiscent of emerald but with higher brilliance, fire, durability, and a total lack of inclusions.
Grossular Garnet & Tsavorite Chemistry, Physical Properties
Grossular Garnet & Tsavorite Optical Properties
Hessonite
Hessonite, which is also known by the name "cinnamon stone," is a brownish-orange grossular garnet that is one of the nine maharatnas (major gems), or navaratna ("divine gems"), which is connected to the Vedic astrological sign of Rahu, or "head of the dragon." Hessonite garnet's Sanskrit name is Gomedhaka.
Bibliography on Grossular Garnet & Tsavorite
1. Swala Gem Traders, Lemshuko Tsavorite Mine near Arusha, Tanzania  . www.swalagemtraders.com
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