Accretions of phosphorite that were deposited under the influence of cyanobacteria on branches and other plant remains. From the Santa Barbara mine on the Tafelberg, Curacao, where large deposits of phosphorite have accumulated from a variety of sources, including bird droppings (guano) and marine invertebrates that secrete shells of calcium phosphate as well as the bones and excrement of vertebrates. These sediments have in the past been mined as a source of phosphates for fertilizers and other applications. Actual image height is 350 mm.