“Marra Mamba” Tiger Eye is a rare variety of Tiger Eye found only in the Hammersley Ranges of the Pilbara region of Western Australia and is widely known as the “Rolls Royce” of Tiger eye. Only two deposits have ever produced “true” Marra Mamba”, a rare type with reds, blues, yellow, gold and greens, often sandwiched between layers of Hematite and Magnetite with red, yellow and green jaspers making is an extremely beautiful gemstone.
Marra Mamba is extremely old, forming when Earth was very young and had little to no oxygen in its atmosphere. Oxygen producing photosynthetic bacteria evolved more than 2700 million years ago and gave off oxygen as a waste product. This oxygen built up in the atmosphere and dissolved in the sea water. When iron, produced mainly from huge submarine volcanoes came in contact with this oxygen, it precipitated as iron oxide in the sea floor and resulted in iron-rich and silica-rich bands, which are now classified as banded iron formations (BIFs).
Burial and heating brought about crystallization of these layers and solutions carrying sodium penetrated through some layers, causing Riebeckite to form. Earth movements throughout the millions of years caused folding and faulting to occur, distortion the layers. Heated fluids passed through the rock and dissolved material and redeposited it elsewhere. The fibrous Riebeckite crystals were replaced by silica with fine dusts of yellow Goethite. These fibrous bands lead Tiger Eye to be classified as a chatoyant gemstone (classification for those minerals with a silky lustre caused by fibrous bands).
About 2000 million years ago, the Pilbara and many other very old pieces of the continental crust were joined together in a supercontinent. When this supercontinent finally began to break up, waters heated by volcanic activity dissolved much silica from the banded iron formation, leaving huge iron ore deposits of almost pure hematite.
Colour Varieties
· White: Quartz SiO2
· Yellow: Goethite Fe2O3
· Red: Hematite Fe2O3
· Blue: Riebeckite Na2FeD[Si8O](OH)
· Green: A mixture of the blue Riebeckite and yellow Goethite
· Black: Hematite FeO3 and Magnetite Fe3O4
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