Serpentine from Sloan Kimberlite

What is the Sloan Kimberlite?

The Sloan Kimberlite group consists of 6 known kimberlite bodies within the State Line district of northern Colorado. At least 4 of the intrusive bodies are diamond-bearing.  Kimberlites are near-surface igneous rocks derived from a magma originating in the Earths’ upper mantle. They are known for their diamond-bearing capabilities… think South Africa and the Northwest Territories of Canada. The Sloan kimberlite contains abundant secondary/alteration minerals, mostly importantly serpentine minerals.

Under the Microscope

The serpentine in this design replaced a rounded grain of what once was a mineral plucked from elsewhere (xenocryst) or a primary mineral from the magma (phenocryst).  We think it’s likely a replacement of olivine.  Now all you see in transmitted, cross-polarized light is the strong contrast of light and dark in large serpentine fibers and an almost vintage greyscale in-between from smaller fibrous grains.