Pyrrhotite inclusions in dark pigmented apatite from granitic rocks
Gottesmann, Barbel; Wirth, Richard
European Journal of Mineralogy Volume 9 Number 3 (1997), p. 491 - 500
published: Jun 2, 1997
manuscript accepted: Nov 19, 1996
manuscript received: Feb 8, 1996
ArtNo. ESP147050903002, Price: 29.00 €
Abstract Combined microprobe, HRTEM, and optical microscopic investigations of the dusky cores of accessory apatite from granitic rocks identified the pigment in these cores as hexagonal pyrrhotite. Pyrrhotite particles are generally below the detection limit of conventional light microscopy, but cause pleochroism of apatite. These inclusions may be very fine-grained (≤ 1 μm) specks or, more rarely, rods. They are rhythmically arranged in layers normal to the c-axis of apatite, separated by nearly inclusion-free zones. Apatite and pyrrhotite are epitactically intergrown, with (1010)apatite 1 1 (0001)pyrrhotite and apatite 1 1 pyrrhotite. Apatite host and pyrrhotite inclusions presumably crystallized simultaneously, forming oriented intergrowths which are favored by the similarity in lattice spacings. The pigmented apatites probably represent foreign material within the granitic magma.