Vivianite from Maryland

Mineral Matters #467

Vivianite, when fresh, can be almost colourless. But when exposed to light, the iron ions (Fe²⁺) in the structure oxidize to Fe³⁺. The colour darkens through green to dark blue, and even black, and the crystals change from transparent to opaque. This process can often eventually lead to the specimen cracking and crumbling.

To preserve the original colour and transparency of vivianite as much as you can, you should keep the specimens covered and out of light except for short periods when they are being viewed.

This specimen has dark blue vivianite crystals in cavities in a vivianite nodule, with the matrix showing cracks. Another specimen from the Charles Willett Collection. The location where these nodules are found is a road cutting. Fossilised shark teeth are also known from here.

Below: Vivianite, Wheeler Road, Oxon Hill, Prince Georges County, Maryland, USA. Width of view 6mm. Click on the image for a higher resolution version.