WAVELLITE
This mineral occurs occasionally as minute, prismatic crystals. It also forms as acicular, radiating aggregates, which are often spherical. Additionally, it forms crusts. The colour is white to greenish white, and green. It forms on rock fracture and joint surfaces as a secondary material. The wavellite photographed above, is Arkansas Wavellite. (Check out Rockhounding Arkansas.)
This wavellite is from just up the road!!
The specimen comes from Highdown Quarry, Filleigh, Devon, UK
And here's a closeup of those radiating aggregates.
Hardness: 3 1/2 - 4