What better for a hot summer’s day than a lovely ball of cooling bluey-green mineral ice cream, whose flavour I shall leave at your discretion. The specimen in the photo displays both common habits of this hydrated aluminium phosphate, spheres and radial sprays (bottom) of needle shaped crystals. Irregular masses can also form, and, very rarely, prismatic crystals.
The usual hue is green, though it can also be yellow, brown or white. It’s named after its discoverer, who found it in an English quarry in 1895. Its geological setting is low grade metamorphism of aluminium rich rocks, at low temperatures and pressures and phosphate rocks that have been altered by mineralising fluids. Wavellite is secondary, formed by the hydration of primary minerals during and after metamorphism. It has sometimes been cut into dome shaped cabochons for collectors, and is used as an ornamental rock. It is found in Arkansas, Bolivian Germany and the original quarry in Devon.
Image credit: Jake Slagle