As part of a research program for recovering alumina from domestic nonbauxitic resources, the Bureau of Mines investigated a lime- sinter, caustic leach technology for anorthosite. This report discusses the unit operations--feed preparation, sintering, and leaching. Acceptable pellets for the bench-scale sintering studies were prepared from mixtures of minus 200-mesh anorthosite and limestone using water alone as the pelletizing agent. Heating pellets at 1,270 deg to 1,360 deg c for periods of 0.5 to 2 hr, followed by a 15-min soaking period at 700 deg c and cooling to room temperature, produced a sinter that dusted to more than 90 pct minus 65 mesh. The weight ratio of limestone to anorthosite was critical in producing sinter exhibiting good dusting and leaching characteristics. A ratio of 2.0 Was optimum for the bulk samples of anorthosite and limestone used in this research. Leach solutions from lower ratio sinters were unstable; gelation became progressively more severe with higher ratio sinters. Leaching the dusted sinter with 10-pct na2co3 at 60 deg c extracted 85 to 90 pct of the alumina in a product solution containing about 50 g/l al2o3. Leach residue in contact with pregnant solution tended to set up as a rigid gel as a result of cementation, compaction, and gelation. The presence of a calcium-sodium zeolite [(ca, na2)6 . (Al2sio4)12 . 27-30H2o] in the ungelled residues seemed to be the main difference between gelled and ungelled residues.