THE CRYSTAL-CHEMISTRY OF SARCOLITE

Physical, crystallographic and chemical data are given for sarcolite in contact metamorphic ejecta from Monte Somma (type locality) and from a second occurrence at Anguillara Sabazia in the Sabatini Mountains, Latium (Italy). The chemical composition can be expressed by the general formula: (Ca,Na)7(Na,K,Sr,Ti,Mn)<1(Al,Mg,Fe)4 Si6O23[(P,Si)O4]0.5 [(CO3)a(SO4)bClc]0.5 (OH,F,H2O)2-a-2b. The presence of SO4 distinguishes the sarcolite from Anguillara Sabazia. There are two types of sarcolite at Monte Somma, one with low P and the other richer in P. Unit-cell parameters are a=12.378(l), c=15.480(8) Å for a sample from Anguillara Sabazia. For the Monte Somma samples a is constant at 12.350 Å, but c ranges from 15.453 (low-P type) to 15.477 Å (P-rich type). The Monte Somma samples have a smaller volume and a greater density. The IR spectra show clear differences in the material, owing to the vibrations of the CO3 group, present only in the Monte Somma samples, and the SO4 group, present only in Anguillara Sabazia samples. Sarcolite coexists with augite, hauyne and fluorite at Anguillara Sabazia and augite, gehlenite and gamet at Monte Somma.