Polarised light micrograph of crystalline phytomenadione Vitamin K3 (Menaphthone). Vitamin K is a fat soluble vitamin which occurs in two forms: phytomenadione (of plant origin) and menaquinone (of animal origin). Its biochemical role is in the formation of prothrombin in the liver: prothrombin is an essential component in the blood clotting process. Dietary deficiency of Vitamin K should rarely occur, since the vitamin is found in both meats and leafy vegetables. Vitamin K2 is synthesized by bacteria in the large intestine. Magnification: X 63 at 35mm size.