Abstract: An oxide or hydroxide mixture or coprecipitate having a three-component oxide composition comprising 5 to 45 mole % of SiO.sub.2, 35 to 65 mole % of ZnO and 0 to 60 mole % of Al.sub.2 O.sub.3 is heated in the presence of water to form a crystal of the fraipontite type.The obtained synthetic mineral has a fraipontite type crystal structure and has a high whiteness and a large specific surface area. For example, this synthetic mineral is valuable as a color developer for a leuco dye.

Abstract: A color developer for pressure-sensitive recording paper which is derived from a clay mineral having a layer-structure composed of regular tetrahedrons of silica and which shows(A) the diffraction pattern attributable to the crystals of layer-structure composed of regular tetrahedrons of silica when subjected to an electron diffraction analysis, but(B) substantially no diffraction pattern attributable to the crystals of said layer-structure when subjected to an X-ray diffraction analysis, and which(C) contains as the constituting elements besides oxygen, at least silicon, magnesium and/or aluminum.This color developer is produced by acid-treating a clay mineral having a layer-structure composed of regular tetrahedrons of silica until its SiO.sub.2 content reaches 82-96.5% by weight on dry basis (drying at 105.degree. C.