Exsolution in metamorphosed chromite from the Red Lodge District, Montana

Three textural types of exsolved chromites. Type A grains consist of an Al-rich host that contains blebs and rare smaller lamellae of an Fe-rich guest; type B grains have an Fe-rich host that contains blebs and dense networks of lamellae of an Al-rich guest; type C grains contain a very fine intergrowth of Al- and Fe-rich lamellae. Miscibility gap in the spinel prism is tunnel-shaped and extends from the Fe3O4-FeAl2O4-FeCr2O4 face to the MgFe2O4-MgAl2O4-MgCr2O4 face. If exsolution began at or near the peak temperature of regional metamorphism in the eastern Beartooth Mountains, the temperature of unmixing was near 600°C.—Modified journal abstract.