Inorganic blue pigments in which manganese (in the pentavalent oxidation state and in a tetrahedral coordination) is the chromophore have been employed since the Middle Ages (e.g., the fossil bone odontolite, which is isostructural to the apatite structure).[22][23] Synthetic alternatives, such as barium manganate sulfate (or Manganese Blue, developed in 1907 and patented in 1935), have been phased out industrially due to safety and regulatory concerns,[24][25] hence YInMn Blue fills the niche of an inorganic, environmentally safe alternative for the traditionally used blue pigments, and offers a durable intense blue color.[1]