Iron Ores of Sedimentary Origin
Ø The iron ores form beds or layers of variable thickness that occur interstratified with other sedimentary rocks.
Ø Sedimentary iron deposits are regarded having formed chiefly as chemical precipitates in the form of oxides, carbonates and silicates from marine waters rich in corresponding salts.
Ø Metasomatic replacement has also been suggested as another important process for formation of many iron ore deposits.
Ø It is also suggested that certain type of bacteria play considerable role in the precipitation of iron.
It is a sedimentary rock composed of the mineral of the same name-gypsum, which has a composition of CaS04.2H2O.
Its common colour is white but it may also occur in other shades such as yellow, red or dark grey due to impurities present in the rock.
Gypsum is formed in nature as a result of evaporation from sea-waters rich in sulphate salts.
ANHYDRITE is a granular aggregate of mineral anhydrite, CaS04' and is geneticallyrelated to the mineral gypsum: hydration of anhydrite results in gypsum.
These rocks are commonly associated in occurrence
Uses: Gypsum finds extensive uses in many industries, e.g.
(i) as a raw material in the manufacture of fertilizers;
(ii) as an essential ingredient in the manufacture of Cement;
(iii) in the manufacture of Plaster of Paris.
(iv) as fire proofing component of gypsum boards.