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Frontier District Sapphires

Geology and gemstones in Kenya's arid northern wilderness

Frontier District Sapphires

One of the most breathtaking safari destinations in East Africa is Kenya’s Northern Frontier District (NFD), an area of spectacular landscapes, rich in striking topographical features, and steeped in complicated, yet fascinating geological history.
This arid wilderness area is home to the Nilotic Samburu and the Cushitic Boran and Oromo tribes who have learned to survive in this harsh region as nomadic pastoralists for over 200 years, moving their cattle, camels, goats, and sheep through the seasons in search of grazing and water.
The region is also a fascinating ecosystem of remarkable flora and fauna, and is well known for its elephant population, and distinctive dry country species such as the Reticulated Giraffe, Grevy’s Zebra, Oryx and Gerenuk.

The NFD stretches east of the Great Rift Valley and north from Kenya’s central highlands of Mt Kenya, and the Nyambeni Hills, beyond which the land drops in elevation to as low as 1,000ft in some areas.

The arid terrain has numerous iconic inselbergs or 'island mountains', basement rocks towering above the surrounding shallow valleys and plains throughout the NFD, such as Ol Lolokwe, Koitogor and Mt. Bodech.

Inselbergs of igneous crystalline rocks are smoothly rounded, typically seen in the NFD where granite is the predominant basement rock. Inselbergs are formed when the surrounding ‘softer’ rock is eroded away, generally by fluvial action and mass wasting, leaving behind protruding remnants of igneous mass.

In addition to these basement rocks, there is plenty of evidence of far younger volcanic rocks such as the lava flows in Shaba, and the well known 'Champagne Ridge' in Buffalo Springs.
These volcanic lava rocks weather down to the grey basaltic soils, quite in contrast to the reddish, crystalline soils derived from the igneous basement rocks, or the fine white chalky soils that are remnants of lake beds.

It was this magma that through volcanic activity was forced to rise and intensely heat the ancient basement rock minerals (such as gneisses and schists) it came in contact with, causing them to metamorphose and re-crystallize into much rarer minerals such as sapphires.

Raw Sapphire - image courtesy of Lapigems Gem CompanySapphires can be found in both igneous and metamorphic rocks, including granite, gneiss, and schist among others. They may also be found in deposits of alluvium.
Sapphires are the second hardest natural mineral known to man. Naturally occurring sapphires are hexagonal crystals called corundum, which is Aluminium Oxide (Al2O3).
During the formation of corundum through shifts in heat and pressure in igneous and metamorphic rocks, the presence of certain minerals will affect the colour of the sapphire. For instance, if iron is present, sapphires may have a green or yellow hue to them, whereas the presence of vanadium can lead to purple sapphires. These coloured gems are known as 'Fancy Sapphires'.
The most well known sapphires are a deep blue colour, which occurs as a result of titanium being present when the rock metamorphosises.

Several hundred million years ago in the rocks of the area we now call the NFD, liquid magma was forced up through the surrounding crystalline igneous granite, the intense heat caused a change or metamorphism in the older rock it came into contact with, recrystallising over millions of years into minerals that were stable at the high heat - in certain parts, changing the ancient granite into sapphire.
These sapphires would remain deep underground for millions of years more, until the weathering of the softer rock above them left them exposed at or near the surface.

Oval cut Sapphire - mage courtesy of Lapigems Gem CompanyThere are only a few places on the planet where these geological conditions exist, and Garba Tulla in the NFD is one such place. Among the weathered plains between the inselbergs sapphires may be found, where, after eons in the making and centuries among Northern Kenya’s wildlife, man was to discover this beautiful stone.

Sapphires have been mined in small quantities in this region over the last 50 or so years. To read about the early days of these mines, please read this fascinating article about Mining in Kenya’s Wilderness written by Antony Zagoritis of Lapigems Gem Company, an East African authority on gemology.

You can learn more about Fancy Sapphires here, or view the cut Fancy Sapphire gemstones mined from the region on their website, as well as the sapphire jewellery that is the latest chapter in a formation process that has taken over 100 million years.

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Nic Cahill

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