Allophane
Since it has short-range atomic order, it is a mineraloid, rather than a mineral, and can be identified by its distinctive infrared spectrum and its X-ray diffraction pattern.Allophane is a weathering or hydrothermal alteration product of volcanic glass and feldspars and sometimes has a composition similar to kaolinite but generally has a molar ratio of Al:Si = 2.Its structure has been debated, but it is similar to clay minerals and is composed of curved alumina octahedral and silica tetrahedral layers.It forms waxy botryoidal to crusty masses with color varying from white through green, blue, yellow, to brown.It was named from the Greek allos – "other" and phanos – "to appear", as it gave a deceptive reaction in the blowpipe flame in old mineralogical testing.