Allophane

Allophane, a rare but interesting mineral, a hydrated aluminium silicate. It is not crystalline, but occurs in reniform or botryoid masses, white, yellow, red, brown, blue, or green in colour, traces of copper and iron oxide being present. It is waxy and translucent, and breaks with a conchoidal fracture. It is found in crevices near the top of the chalk at Charlton and Burham in Kent, at Beauvais and at several German localities. It is suggested that allophane, and the silicate of iron forming the green coating of the flints resting on the chalk, have originated from the superincumbent clay, or that in the chalk, with iron oxide and water.