The stones

Ruby is what this ground produces.

Rockland mines one gemstone: ruby, from the John Saul Ruby Mine in Tsavo West. The belt around the mine carries several others. This page sets out what the stone is, and what the company does and does not mine.

01 Ruby

Corundum, coloured by chromium.

Ruby is the red variety of corundum, which is aluminium oxide. Chromium in the crystal produces the colour, and the stone has a hardness of 9 on the Mohs scale. Sapphire is the same mineral in every colour except red.

At John Saul the deposit sits in an altered ultramafic body within gneiss and schist. Chromium is high and iron is low, which gives the stones strong saturation and a fluorescence that has often been compared with ruby from Burma.

Ruby from the John Saul mine can be distinguished from ruby mined elsewhere.

Species
Corundum
Formula
Al2O3
Colour
Red, from chromium
Hardness
9 on the Mohs scale
Specific gravity
4.00
At John Saul
High chromium, low iron
Two red ruby crystals and a smaller pink crystal standing in a dark matrix with small blue kyanite blades below.
Ruby crystals in matrixReference specimen, Tanzania
A white tray of screened gravel on a sorting table, with rough stones visible among the wash, and a sorter's hand at the edge of the frame.
Rough ruby on the sorting tableJohn Saul Ruby Mine

02 The belt

The belt runs from Mozambique to the Kenyan coast.

The East African Gemstone Belt is known in geological terms as the Mozambique Metamorphic Belt. It is a continental-scale structure, and its settling ended about five hundred million years ago. Its geology is similar to that of Madagascar and Sri Lanka, and the belt runs from Mozambique through Tanzania to the Kenyan coast.

At John Saul the deposit lies inside Tsavo West National Park, in Taita Taveta County, in semi-arid country covered with thorn bush. The mine is reached through the Kenya Wildlife Service gate at Kasigau.

Belt
Mozambique Metamorphic Belt
Extent
Mozambique, Tanzania, Kenya
Settling ended
About 500 million years ago
Kenyan county
Taita Taveta
Park
Tsavo West National Park

Sourced

Taita Taveta is considered the resource hub for gemstones in Kenya. That assessment is the Ministry of Mining's, quoted in the company's own material.

03 The others

The belt carries other stones.

Three coloured stones share the belt with ruby: tsavorite, tourmaline and garnet. Rockland's published material describes ruby only, and the company does not mine these. They are set out here because a buyer looking at Kenya will meet them.

Tsavorite takes its name from Tsavo East National Park. The green garnet was found in Tanzania in 1967, in Kenya in 1971, and named after the park by Tiffany and Co in 1974.

Not mined here

Tsavorite, tourmaline and garnet are worked in the belt by other operators. Rockland's material describes ruby only, and this page does not present the other stones as the company's own.

A spread of small faceted tsavorite garnets, green and pale green, on a white surface.
Tsavorite garnet, facetedAdam Kelliher, CC BY-SA 4.0
A cushion-cut rubellite tourmaline, deep pink to red, with visible internal inclusions.
Rubellite tourmaline, facetedJames St. John, CC BY 2.0
Coloured stones of the Kenya and Tanzania belt
Stone Species Colour from In Kenya
Ruby Corundum Chromium Mined at John Saul since 1991
Tsavorite Grossular garnet Vanadium and chromium Named after Tsavo East; Kenyan deposit found in 1971
Tourmaline Tourmaline group Iron, manganese and copper The belt carries tourmaline mines
Garnet Garnet group Iron, chromium and others The belt carries garnet mines; rhodolite is the rose-red variety
Sapphire Corundum Iron, titanium and vanadium Listed among Kenya's gemstone exports

04 Value

A stone is judged on five factors.

Stones are graded at the mine into three levels. The factors below are the ones the company's own material names, and size is judged separately, because buyers often want parcels of matching size.

  1. 01

    Variety

    What the stone is. Ruby is the red variety of corundum.

  2. 02

    Carat weight

    The weight of the stone, in the unit used for coloured stones.

  3. 03

    Colour

    The hue and tone. At John Saul the colour comes from high chromium and low iron.

  4. 04

    Saturation

    The strength of the colour, which this deposit is known for.

  5. 05

    Clarity

    How free the stone is of inclusions that show.

Credits

About the photographs on this page.

The sorting floor photographs are the company's own, taken at John Saul. The specimen photographs are licensed reference images of the mineral species, not stones from this mine, and each is credited under the picture.

Ruby: StrangerThanKindness, CC BY-SA 3.0 · Tsavorite: Adam Kelliher, CC BY-SA 4.0 · Tourmaline: James St. John, CC BY 2.0

Mineral facts come from the Gemological Institute of America's gem encyclopedia. The tsavorite history and the description of the belt come from Wikipedia. Licence details for the specimen images are in photos/licensed/CREDITS.md.

The Rockland story

The discovery, the lease, the geology and the mining method.