Cornish Serpentine & Whitby Jet

Cornish serpentine is the name given to the green and red marble like decorative stone found on the Lizard Peninsular of Cornwall. The rocks of the Lizard complex are of extreme geological important being Britain’s only ophiolite suite. An ophiolite complex is formed when rocks derived from the earth’s mantle are thrust faulted up over younger rocks exposing the junction between the crust and the mantle, the moho, at the surface. This gives a valuable insight into the mantle composition and is only found at a few other locations worldwide. The rocks known as serpentine today, were originally upper mantle peridotites composed of olivines and pyroxenes. These rocks were present below the sea of a small rift valley similar to the Red Sea today. 350 Million years ago during the Devonian the continental plates either side of the ocean began to converge. Unusually one of the plates was obducted and lifted over the top of the younger rocks below bringing mantle rocks to the surface These rocks have undergone serpentinization, in which the hydrothermal alteration of the minerals by percolating seawater causes them to be replaced by serpentine minerals largely clays, chlorite, tremolite and talc. Iron minerals such as goethite and hematite are also present and the resulting rock has a multicoloured appearance resembling snake or lizard skin. The beauty of these rocks may first have been noticed by local farmers as their cows brushed against rocky outcrops inadvertently polishing them .A small cottage industry was established producing tourist gifts. During Victorian times a sizable industry grew up by royal approval, however this has declined and there are now only a few manufacturers left in the area.

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