Carbo Animalis or Bone Char is a porous, black, granular material produced by charring animal bones. Its composition varies depending on how it is made; however, it consists mainly of tricalcium phosphate (or hydroxyapatite) 57–80%, calcium carbonate 6–10% and carbon 7–10%. It is primarily used for filtration and decolorisation.

Bone char is primarily made from cattle and pig bones; however, to prevent the spread of Creutzfeldt–Jakob disease, the skull and spine are no longer used. The bones are heated in a sealed vessel at up to 700 °C (1,292 °F); the oxygen concentration must be kept low while doing this, as it affects the quality of the product, particularly its adsorption capacity. Most of the organic material in the bones is driven off by heat, and was historically collected as Dippel's oil; that which is not driven off remains as AC/HydroXyapatite/CaCO3 in the final product.

The tricalcium phosphate in bone char can be used to remove fluoride and metal ions from water, making it useful for the treatment of drinking supplies. Bone charcoal is the oldest known water defluoridation agent and was widely used in the United States from the 1940s through to the 1960s. As it can be generated cheaply and locally it is still used in certain developing countries, such as Tanzania. Bone chars usually have lower surface areas than activated carbon, but present high adsorptive capacities for certain metals, particularly those from group 12 (copper, zinc, and cadmium). Other highly toxic metal ions, such as those of arsenic and lead may also be removed.

Bone char carbon is currently one of the most effective methods for the reduction of chlorine, Chloramine, lead, cadmium, mercury, copper, zinc, aluminium, radio-nuclides, radioactive isotopes, fertilisers, uranium, radium, pesticides in Koi ponds.

Note that the presence of Sulphates in the water will shorten the life of the Bone Char as the Calcium HydroxyApatite reacts with the Sulphate.