Apertura della Rift Valley
Provenance
It is not the recent volcano that makes Kenya’s gems, but the ancient rock the African rift lifted to the surface. Our stones are born there: in the metamorphic basement of the Mozambique Belt, along the Taita-Taveta block.
Why the Rift Valley
The Rift Valley you see is young. The gems it yields are half a billion years old.
The rifting of East Africa is a recent phenomenon: the Nubian and Somali plates drift apart by a few millimetres a year, and in doing so they have raised highlands and carved the trench that runs across Kenya. But the gems do not come from that young tectonics. They come from the rock the Rift has cut and laid bare: the Mozambique metamorphic belt, a Neoproterozoic basement formed between 750 and 540 million years ago.1
This is why a thin band of southern Kenya concentrates ruby, sapphire, green garnet, tourmaline and aquamarine. The country’s mineral heart is the Taita-Taveta block (Voi, Kasigau, Kuranze, Mwatate and the Taita Hills), beside Tsavo National Park.4
The gem belt
Geologists call it the Mozambique Belt, or the “East African gemstone belt”: a metamorphic chain running from Somalia to Mozambique and Madagascar. Its gems formed during the East African–Antarctic orogeny, the collision between the eastern and western blocks of Gondwana that closed the Mozambique Ocean.
750–540 Ma
The age of the Neoproterozoic basement that hosts the deposits, from Somalia to Madagascar.1
650–550 Ma
The window in which tsavorite formed, as eastern and western Gondwana welded together.1
Taita-Taveta
The key block: graphitic gneisses and calc-silicates with meta-evaporites, the protoliths of an ancient sabkha coastline.1
The main stones
Each stone carries its real locality, its mineral species and, where it exists, the documented story of its discovery. The images are rough crystals photographed like specimens: the colour is the stone’s true one.
Taita-Taveta, Voi
grossular garnet, green from vanadium
Campbell Bridges found the green garnet in 1967 on the Tanzanian side and secured a deposit in Kenya in 1971. Henry Platt, president of Tiffany & Co., named it “tsavorite” in 1973 after Tsavo Park; Tiffany’s 1974 campaign brought it to market.2
Kenyan green
Mangare, Tsavo West
corundum, red from chromium
In 1973 geologists John Saul and Tim Miller, hunting for chromium- and vanadium-coloured gems, found the John Saul (Rockland) mine in the Mangare area. The ruby forms in the metasomatised contact zone between an ultramafic body and the gneisses; new finds are coming from Baringo.3
Corundum
Dusi, Garba Tula
corundum, blue, green and yellow
The Dusi deposit (Garba Tula), in central Kenya, is described in the peer-reviewed scientific literature and yields blue, green and yellow sapphires. Baringo also produces pink sapphires, from the same settings as the rubies.5
Corundum
Kenyan coast, Kwale
blue beryl
Kenya’s coastal belt, in the hinterland of Mombasa between Kwale and Kilifi, gives clear pale-blue aquamarines, prized for their transparency. They come from the pegmatites of the same mineral province.6
Beryl
Taita Hills
green, pink and bicolour
Taita-Taveta county produces green, pink and bicolour tourmalines. They appear in the same pegmatites and metamorphic rocks of the Taita-Taveta block that hosts tsavorite and garnets.6
Tourmaline
Kuranze, Taita-Taveta
pyrope-almandine garnet
Kenya’s rhodolite garnet has a purple-red leaning to raspberry. The Kuranze deposits, in the Taita-Taveta block, are an important source of this variety.6
Garnet
The truth about provenance
Selling provenance also means knowing where fact ends and marketing begins. Three things we state with precision, and that others confuse.
Not Kenyan
Tanzanite comes from Merelani, in Tanzania, the world’s only commercial source since 1967. It is not a stone of the Kenyan Rift. When we handle it, we state its real origin.7
No Kenyan source
Kenya is not a confirmed source of emerald. The Kenyan green is tsavorite, a garnet: we do not pass it off as emerald. If a client wants emerald, we state its true origin.
What the lab says
For coloured stones there is no Kimberley Process. Laboratories state the country or area, not the individual mine. We state origin only when we can stand behind it.8
Sources
