Allanite-(La) from Buca della Vena Mine, Apuan Alps, Italy; an epidote-group mineral

Allanite-(La) occurs as black prismatic crystals up to 2-3 mm in length along [010], in baryte veins cutting a dolomitic metamorphosed limestone at Buca della Vena mine, near Stazzema, in the Apuan Alps, Tuscany. It has a vitreous lustre and is transparent to translucent, with imperfect cleavage along {001}; H. approximately 6, D 3.93 g/cm (super 3) ; alpha 1.735, beta 1.760, gamma 1.765, 2V (sub alpha ) 90 degrees , with very high dispersion and strong pleochroism from greenish to greenish brown. EPMA results are given and lead to the simplified formula Ca(REE,Ca)Al (sub 2) (Fe (super 2+) ,Fe (super 3+) )(SiO (sub 4) )(Si (sub 2) O (sub 7) )O(OH). Indexed XRD powder data are tabulated; strongest lines 2.901(100), 2.692(60), 2.611(50), 2.860(40), 2.174(25) Aa; a 8.914, b 5.726, c 10.132 Aa, beta 114.87 degrees , V 469.1 Aa (super 3) , Z = 2, space group P2 (sub 1) /m; the crystal structure has been refined to R 0.0328. The name allanite-(La) recalls the relationship with allanite-(Ce), and fills a gap in the systematics of the epidote group.