LARGE MARRA MAMBA TIGER EYE SLAB. ...

Description

LARGE MARRA MAMBA TIGER EYE SLAB
Mt Brockman Station, Western Australia
Tiger eye is an ancient rock, formed from sediments laid down at the bottom of a shallow sea over two and a half billion years ago, when the early Earth's atmosphere had little or no oxygen. Sometime later (approximately 2 billion years ago) the first photosynthetic bacteria evolved and began to give off oxygen as a waste product, which built up in the atmosphere and dissolved in sea water. When this came in contact with iron (produced mainly from huge submarine volcanoes), it precipitated as iron oxide in the sea-floor mud and resulted in the iron- and silica-rich bands now classified as a banded iron formation (or BIF). Other minerals were also present and heating and burial bought about the crystallization of these layers; it seems likely that solutions carrying sodium penetrated along some of the layers and this is where the mineral riebeckite was formed. The fibrous riebeckite variation with which Tiger eye originates is known as crocidolite, or blue asbestos, but pseudomorphically replaced by silica, with a fine dust of yellow goethite outlining the shape of the original crystals; this is the same way in which fossil wood preserves the outline of cells and growth rings. Tectonic activity throughout millions of years caused crumbling, folding and distortion to the layers of sediments. At the same time, heated watery fluids passing through the rock dissolved some of the material and redeposited them elsewhere. This terrific slab is a perfect illustration of these millions of years' worth of geological processes, a wonderful natural canvas of abstract art with bands of deep olive and bottle green, blood red and metallic black mingled with shimmering golden tiger eye and orange-brown limonite (goethite with other hydrated iron oxides such as lepidocrocite or jarosite) to incredible effect. Left with a naturally contoured edge, this beautiful slab measures an impressive 55½ x 19½ x 1 inches.

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