Durangite from the Black Range, New Mexico, and new data on durangite from Durango and Cornwall.

Durangite, associated with cassiterite, hematite, quartz, tridymite, cristobalite and clinopyroxene, occurs in small veinlets within flows, ash-flow tuffs and lithic tuffs in a tin mine near Boiler Peak, New Mexico. It is clear to semi-translucent, pale yellow-orange to medium orange-red with a vitreous lustre, pale yellow streak; H. 5-5.5%; irregular to conchoidal fracture and a good (110) cleavage; elongate along c with (110), (010), (021) and (111) the prominent forms; Dmeas 3.90, Dcalc 3.92 g/cm3; alpha medium yellow orange 1.634(3), beta pale yellow orange 1.663(3), gamma colourless 1.685(3); weak to moderate dispersion r < v. The structural formula is: (Na0.93Li0.07)SIGMA 1.00(Al0.89Fe0.07Mn0.06)SIGMA 1.02As0.99O4(F0.90(OH)0.07)SIGMA 0.97. Indexed XRD powder data are tabulated; a 6.574(1), b 8.505(2), c 7.019(1) A, beta 115.34o; space group C2/c; Z = 4. Additional X-ray and chemical data on durangite from Durango and Cornwall are also included.-L.T.T.