The sedimentary phosphates from Ceru Colorado ("red hill"), Aruba, are composed of siliciclastic debris (mainly quartz), derived from nearby weathered quartz diorites, and different types of calcareous grains which have an in-basin origin (bioclasts, fetal pellets, intraclasts). Before denudation took place, bird guano had already phosphatized the debris. Fluorapatite and crandallite are the dominant phosphate minerals. Within the depositional basin, reworking by mechanical and biological agents was a common phenomenon. Elevation of the deposit above sea level was followed by a secondary phase of guano-induced phosphatization, which resulted in the generation of minor amounts of monetite, brushite, and leucophosphite.