An oxide or hydroxide mixture or coprecipitate having a three-component oxide compositn comprising 5 to 45 mole% of SiO 2 , 35 to 65 mole% of ZnO and 0 to 60 mole% of Al 2 O 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.