The dataset includes .csv spreadsheets which provide whole rock geochemical data for the alkaline silicate and carbonatite samples from which apatite and monazite were analyzed, as well as geochemical data collected via electron microprobe and laser ablation ICP-MS for the apatite and monazite mineral grains. Whole rock geochemical data were collected by SGS Labs, except carbonatite samples 84-6-125, 85-1-162, 85-9-157, 85-12-304, and 85-12-317, which were collected by AGAT Labs. The .csv files containing geochemical data are associated with individual data dictionaries that define the columns in each file. Additional .csv files are included summarizing reference material analyses, detection limits, and analytical error for electron microprobe and laser ablation ICP-MS analysis. This data release also includes back-scattered electron (BSE) images of apatite mineral separates in epoxy grain mounts from samples collected in outcrop from alkaline silicate rocks of the Mountain Pass Intrusive Suite, as well as apatite and monazite in thin section in samples of drill core from the Mountain Pass carbonatite (the Sulphide Queen orebody). The zip file Phosphate_Mineral_Images contains all BSE images, organized into separate folders for apatite and monazite with subfolders for each sample. The file name of each photograph correlates to the date the image was taken, the mineral imaged, and the sample, mineral grain, and spot identification. The zip file CL_Images contains all mixed RGB hyperspectral cathodoluminescence images and element maps for Sr, Na, and Ce (apatite) and Ca, Si, and Th (monazite). The file name correlates to the sample number, grain number (as in Phosphate_Mineral_Images), and type of data displayed. Acquisition parameters for element map data are displayed on element map images.