Picture a remote valley in northern Tanzania sandwiched between a spread of sandy brown hills - with the profile of a bull's humped back. This shape that the tribesmen call "njaro". The month is February, the end of the blistering east African dry season. A lone figure struggles through a copse of Sansivera, the wild African sisal, whose sword-spike leaves can cut a man's skin to ribbons. This is the domain of the Tsetse fly, of Kifaru the rhino, and of Simba the hunting lion.

The man lifts his head and surveys the parched savannah then, lowering his head, resumes walking. His feet trace a precise grid pattern; his eyes carefully scan the cracked earth. Then, he pauses mid-step like a thoroughbred hunter on point. Raising his head, he removes his bush hat, squints, shakes his head and wipes the sweat from his eyes. Hunching over, his trained eye detects just the slightest hint of green twinkling in the equatorial sun. His breath catches in his throat; he squats down to get a better look. Yes! Here they are, crystal shards, brilliant as tiny green diamonds. The search is over! But, the real work has just begun...

Geologist Campbell Bridges found the first commercially exploitable deposits of Tsavorite in 1968, thirteen miles southeast of the Tanzanian village of Komolo. He was not surprised-- he had found the first traces of the gem in Zimbabwe in 1961!

Photo: R. W. Wise Geologist Campbell Bridges gives a tour to Rebekah Wise. This tunnel (adit) at the Scorpion Tsavorite Garnet mine burrows several hundred feet into the remains of an ancient coral reef. Voi, Kenya.

Tsavorite, technically a calcium aluminum silicate that crystallizes in the cubic system, is a green grossular garnet. As in emerald, trace amounts of vanadium and chromium account for the green hue. Grossular is one of six members of the garnet family that includes pyrope, almandine, andradite, uvarovite and spessartite. Tsavorite is not the only member of the grossular species; it can occur in a range of colors including yellow, orange, pink, and brown. Grossularite was originally named for the gooseberry stone-- a yellowish orange garnet.

Green grossular garnet occurs in a geological formation known as the Mozambique belt. Consisting of high-grade metamorphic rocks, this belt stretches three thousand miles up the east coast of Africa from Mozambique in the south-southeast through the countries of Tanzania, Kenya, Ethiopia and Sudan. The rocks of the Mozambique belt are a diverse mix of volcanic rocks, ancient sediments and intrusions that have endured several metamorphic phases, entirely altering the original character of the rocks.

COLOR CONSIDERATIONS

HUE:

Bridges has identified three mixtures of hue that, in his opinion, describe the finest colors in tsavorite garnet; these are: forest, water and grass green. Forest green is visually bluish, 85-90% green, 10-15% blue. Water green appears a bit yellowish; 75% green, 15% yellow and 10% blue. Standing between the two is grass or leaf green, a visually pure green that contains 80% green hue with approximately equal amounts of yellow and blue.

In fact, the market tends to favor slightly bluish-green stones. Unlike African emerald, tsavorite is never over-blue. Like emerald, yellow is the bane of this green grossular garnet. Ten percent or more yellow begins to visually dilute the green. As a general rule of thumb, gems that are visually yellowish should not be considered top color.

SATURATION:

Saturation or intensity of hue is rarely a consideration in evaluating tsavorite. Occasionally a slight admixture of gray will mask the normally vivid hue and this will affect value, but, tsavorite more often than not, a bright or vivid hue.

TONE:

Photo: R. W. Wise A lordly bull elephant surveys his domain. Serengeti National Park, Kenya.

To be considered tsavorite, a gem must have at least medium or 60% tone. Stones with tonal values below 60% have a watery or pastel appearance and are called green grossular garnet. 75-85% tone is considered optimal. Stones with tonal values above 85% appear overdark.

The division of color in gemstones into hue, saturation and tone is useful in discussion. In practice, beauty is a balance between these abstractions in which clarity and cut also play a part. In tsavorite, for example, the addition of yellow to green yields a lighter tone and a more vibrant color. The addition of blue yields a richer hue that is also darker in tone.

CLARITY:

Tsavorite like most colored stones is graded by eye without the aid of a loupe. A flawless stone is one with no visible inclusions. The Guide classifies tsavorite as a type II meaning larger stones may have eye visible inclusions. Tsavorite prices are markedly affected by the presence of any inclusions that are eye visible. Gems with visible inclusions are marked down a minimum of 20% and more depending on the size and placement of the inclusions. Included stones are often cut en cabochon. Cabochon tsavorite sells for approximately 25% of the price of a comparable faceted stone.

CUT:

Those who persist in comparing tsavorite to emerald will always favor the classic emerald cut. Tsavorite has a higher refractive index and double the dispersion of emerald, giving it potentially much greater brilliance. The emerald cut's fifteen to seventeen relatively large facets restrains the natural sparkle of the garnet, giving it an appearance that bears an uncanny resemblance to the satiny brilliance of emerald. However, cutting in the brilliant style releases the garnet's full potential, allowing it to stand toe to toe when set with diamond. Tsavorite mining is clustered in an area northwest of Mombassa, within a twenty-five mile radius of the Kenya

Tanzania border. In 1990 another source of tsavorite was located in Turkana in northwestern near the Uganda border. Mining commenced in this area in 1994. Gems mined at Turkana are generally larger and darker in tone, perhaps due to a relatively higher chromium content, than those found in the south. Towards the end of 1991 a deposit of vanadium rich tsavorite was discovered the Gogogogo area of southwestern Madagascar about 40km north of Ampanihy. Given the extent of the Mozambique belt other deposits of this type garnet undoubtedly exist.

Supply.

Photo: R. W. Wise Masai woman.

Tsavorite is rare in sizes above three carats and generally unavailable in the market in sizes above five carats. According to Bridges, who has devoted the past twenty five years to mining the stone, approximately 85% of material mined yields stones under one carat, 10% yield stones above one carat, 2.5% over two, 1% over three. Stones over ten carats comprise about one tenth of one percent of total production.

Ironically it is tsavorite's extreme rarity that keeps prices for larger sizes from increasing geometrically in price. In the early 1970s Bridges offered Tiffany & Co. an exclusive marketing arrangement. Henry Platt, Tiffany's president and the man who gave the new green garnet its name, demurred, because quantities of larger stones sufficient to launch a profitable marketing campaign could not be guaranteed.

One writer recently described tsavorite as the Demantoid garnet of the Twentieth Century. Given the beauty of the stone and the extensive area of the geological belt that contains it, reports of the imminent demise of tsavorite can be said to be greatly exaggerated.