(i) In sedimentary rocks a number of minerals occur in beds or layers.
(ii) They have been formed as a result of deposition, accumulation and concentration in horizontal strata.
(iii) Coal and some forms of iron ore have been concentrated as a result of long periods under great heat and pressure.
(iv) Another group of sedentary numerals such as gypsum, potash salt and sodium salt are formed as a result of evaporation.
