Abstract: This paper reports the first in-situ finding of perrierite-(Ce) in Latium. The mineral occurs as brownish-red, transparent, well-developed, euhedral, prismatic crystals inside the miarolitic cavities of a holocrystalline ejectum from La Mola, Monti dell'Anguillara district, Sabatini volcanic complex.
The cell parameters (from Gandolfi film) are (in Å): a = 13.629(9), b = 5.727(1), c = 11.715(6), β(°) = 113.74(2), V(Å3) = 835.5(9). The crystal-chemical formula, based on microprobe analysis of one grain, is: (Ca1.882Th0.124REE2.021Y0.024)(Fe0.9282+Mg0.072)(Ti0.735Al0.632Zr0.484Nb0.019Mn0.033Mg0.045)Ti2(Si3.911Al0.089)O22.
This perrierite is the most Zr-rich described so far. The entry of Zr in the C site of the structure is related to the substitution of large amounts of Ca in the A site, according to the charge balancing relationship: CaA2++(Ti4+,Zr4+)C=REEA3+
The genesis of perrierite-(Ce) from La Mola is linked to late pneumatolitic-pegmatitic hypabyssal stages of the regional volcanic activity.