Are all clay minerals hydroxide(OH) minerals?
Answer Clay minerals are formed by chemical decomposition of pre-existing silicate minerals.The most wide spread are the clay minerals ,which are hydroussilicates all with the phyllosilicate structure and with very small grain size generally less than 0.004mm in diameter and ranging down to colloidal dimensions. The commonest clay minerals are kaolinite,montmorillonite,illite and chlorite and they often occur together in a pariculur sediment.(Berry,1974) Kaolinite is formed by the decomposition of orther aluminosilicates partculurly feldspars .Kaolinite is industrial mineral used in paper indistry ,silk industry,plastics etc due alteration of minerals Gypsum -caso4.2H20-is FORMED AS EXTENSIVE SEDIMENTARY DEPOSITS INTERBEDDED WITH LIMESTONE ,RED SHALES ,SAND STONES ,CLAY AND ROCK SALT.It isnormally the first salt deposited in the evaporation of sea water followed by anhydrite and halite as the salinity increases which are followed ,in rare cases by more soluble sulfates and other salts
