A Note on the Chemistry and Mineralogy of Apatite Crystals of Eppawala and Ridigama Phosphate Deposits

Abstract

The mineralogy, chemistry and solubility of apatite from two rock phosphate deposits in Sri Lanka were studied. The larger deposit is located at Eppawala in the North Central Province, and the newly discovered smaller deposit is at Ridigama, iri the North Western Province. Both ores show enrichment of phosphorous by way of primary and secondary components, developed in two stages. The primary component consists of coarse, primary apatite crystals, whereas the secondary component has a finer matrix. The primary apatite crystals of both deposits contain at least two types of apatite: chloro-fluoro-hydroxylapatite (CFHA) as the major type and fluorapatite (FA) as the minor one. Although the mineralogical composition of the primary apatite of the two deposits is similar, their a-axis dimensions are different. Further, it was revealed that the crystal structure of the primary apatite from Eppawala is more stable than that of Ridigama. Therefore, a greater Chemical reactivity is expected of the primary apatite from Ridigama than that from Eppawala. This explanation is consistent with the solubility data obtained for the primary apatite of two deposits, primary apatite from Ridigama being more soluble than that from Eppawala. In addition, Chemical studies show that the primary apatite from both locations, with low Fe and Al contents, has a better potential as a fertilizer than that of their finer matrices.