Anyolite

Anyolite is a metamorphic rock consisting of a granular mass of bright green chrome-zoisite with minor very dark green pargasite (commonly both as grains a few mm diameter), containing conspicuous coarse porphyroblasts of purplish red corundum (var. ruby) which may be up to several centimetres across.

As a generic petrographic description of this rock would be like corundum-pargasite zoisiteite. But it has been given a more euphonious name, Anyolite, from the word for green in the native language (anyoli) of the Masai tribe.

Ruby-zoisite was discovered in 1954 at the Longido mining district in northeast Tanzania by Tom Blevins, an English prospector. To this day, Tanzania remains the only source for ruby-zoisite. Blevins had initially thought that he had found vast ruby deposits in 1949, but it later turned out to be a green zoisite matrix with large inclusions of mostly opaque ruby. Ruby-zoisite is also heavily included with black hornblende minerals.

The Longido mine (Fig.1) is located in the northern province of Tanganyika territory. The outcrops occur in the highly metamorphosed basement complex which forms small hills (The Matabatu Mountains) descending, at their margin, by step-faulting to a peneplaned surface cut out of much younger, unconformable volcanics. The basement rock adjacent to the zoisite-ruby rocks is usually an amphibolite with conspicuous large, brown-red garnets. The occurrence of this garnet-amphibolite is usually an indication of the proximity of the zoisite-ruby rocks. The outcrops of the zoisite-ruby rock are small. The largest is just over 100 yards long and about 50 yards wide. The foliation corresponds with that of the surrounding metamorphic types. It is, therefore, difficult to determine whether the zoisite-ruby rock is a highly altered intrusive rock or whether it has been formed by metasomatism or is a migmatic product. Probably each of these processes has played a part in its production.

The zoisite-ruby rocks shows a continuous gradation from a very dark amphibolite containing very little zoisite to a much paler applegreen, zoisite-rich rock with little amphibole, but usually containing large, red corundum crystals (var. Ruby). The schistosity of the zoisite-rich types is poorly defined. In thin sections under the microscope the rock shows the association of corundum, amphibole, and zoisite; some samples sometime show, in addition, a little plagioclase and colourless mica.

Fig.1: Longido mine location.

Anyolite from Tanzania. Green = Cr-zoisite; black = amphibole; reddish = ruby (corundum). From James St. John.

Anyolite from Tanzania. Green = Cr-zoisite; black = amphibole; reddish = ruby (corundum). From James St. John.

Anyolite from Tanzania. Green = Cr-zoisite; black = amphibole; reddish = ruby (corundum). Mundarara Mine (Mdarara), Arusha Region, Tanzania. From Parent GÃ©ry.

Anyolite from Tanzania. Green = Cr-zoisite; reddish = ruby (corundum). Mundarara Mine (Mdarara), Arusha Region, Tanzania. From Parent GÃ©ry.

Bibliography

• Giuliani, G., Ohnenstetter, D., Garnier, V., Fallick, A. E., Rakotondrazafy, M., Schwarz, D., & Groat, L. (2007). The geology and genesis of gem corundum deposits. Geology of gem deposits, 37, 23-78.

Photo
Green chrome-zoisite crystals, pale-green amphibole crystals and pink ruby crystal. Anyolite from Longido mine, Tanzania. PPL image, 1x (Field of view = 9mm)	Chrome-zoisite crystals, amphibole crystals and ruby crystal. Anyolite from Longido mine, Tanzania. XPL image, 1x (Field of view = 9mm)	Green chrome-zoisite crystals, pale-green amphibole crystals and big pink ruby crystal. Anyolite from Longido mine, Tanzania. PPL image, 1x (Field of view = 9mm)
Chrome-zoisite crystals and big ruby crystal. Anyolite from Longido mine, Tanzania. XPL image, 1x (Field of view = 9mm)	Green chrome-zoisite crystals, pale-green amphibole crystals and big pink ruby crystal. Anyolite from Longido mine, Tanzania. PPL image, 1x (Field of view = 9mm)	Chrome-zoisite crystals, amphibole crystals and ruby crystal. Anyolite from Longido mine, Tanzania. XPL image, 1x (Field of view = 9mm)
Green chrome-zoisite crystals and big pink ruby crystal with brown simplectitic structures. Anyolite from Longido mine, Tanzania. PPL image, 1x (Field of view = 9mm)	Green chrome-zoisite crystals and big pink ruby crystal with brown simplectitic structures. Anyolite from Longido mine, Tanzania. PPL image, 2x (Field of view = 7mm)	Chrome-zoisite crystals and big ruby crystal with brown simplectitic structures. Anyolite from Longido mine, Tanzania. PPL image, 2x (Field of view = 7mm)
Green chrome-zoisite crystals and big pink ruby crystal with brown simplectitic structures. Anyolite from Longido mine, Tanzania. PPL image, 2x (Field of view = 7mm)	Green chrome-zoisite crystals and big pink ruby crystal with brown simplectitic structures. Anyolite from Longido mine, Tanzania. PPL image, 2x (Field of view = 7mm)	Green chrome-zoisite crystals and big pink ruby crystal with brown simplectitic structures. Anyolite from Longido mine, Tanzania. PPL image, 2x (Field of view = 7mm)
Chrome-zoisite crystals and big ruby crystal with brown simplectitic structures. Anyolite from Longido mine, Tanzania. PPL image, 2x (Field of view = 7mm)	Green chrome-zoisite crystals and big pink ruby crystal with brown simplectitic structures. Anyolite from Longido mine, Tanzania. PPL image, 2x (Field of view = 7mm)	Chrome-zoisite crystals and big ruby crystal with brown simplectitic structures. Anyolite from Longido mine, Tanzania. PPL image, 2x (Field of view = 7mm)
Pink ruby crystal with brown simplectitic structures. Anyolite from Longido mine, Tanzania. PPL image, 10x (Field of view = 2mm)	Pink ruby crystal with brown simplectitic structures. Anyolite from Longido mine, Tanzania. XPL image, 10x (Field of view = 2mm)	Pink ruby crystal with brown simplectitic structures. Anyolite from Longido mine, Tanzania. PPL image, 10x (Field of view = 2mm)
Fracture in a pink ruby crystal. Anyolite from Longido mine, Tanzania. PPL image, 10x (Field of view = 2mm)	Fracture in a pink ruby crystal. Anyolite from Longido mine, Tanzania. PPL image, 10x (Field of view = 2mm)	Fracture in a ruby crystal. Anyolite from Longido mine, Tanzania. XPL image, 10x (Field of view = 2mm)