Magnesium sulphate. Polarised light micrograph of crystals of magnesium sulphate (MgSO4), a chemical used medicinally and in the textile industry. This chemical occurs naturally as kieserite or reichardite but may also be manufactured by the action of sulphuric acid on magnesium carbonate. In its hydrated form (MgSO4. 7H2O) it is known as Epsom Salts, a bitter-tasting substance used medicinally as a purgative and in hypertonic baths to soothe the skin. Magnesium sulphate also has uses in the textile industry, being used as a dressing for cotton goods and as a dyeing agent. Magnification: x25 at 35mm size.