Phosphatic sediments are of considerable economic importance because, together with certain igneous rocks, they constitute the only raw material suitable for the manufacture of phosphate fertilizers and some phosphorus-based chemicals. They contributed about 84% of the total world production of 125 million tonnes of phosphate rock in 1978. Nearly all the output is from stratified marine deposits in which phosphate is invariably present as carbonate-fluorapatite (francolite). Pelletal textures are characteristic. Quality factors, other than phosphate content, are extremely important in determining commercial viability of individual deposits. Phosphatic sediments are widely distributed, the most important commercially being the Miocene–Pliocene deposits in Florida and the extensive Upper Cretaceous–Lower Eocene formations which form the Mediterranean Phosphate Province. Also being exploited are marine sediments of Precambrian, Cambrian, Ordovician, Permian and Jurassic age.