Oxalosis. Light micrograph of a section through adult bone tissue affected by oxalosis (primary hyperoxaluria), showing mature bone (green), newly formed immature bone/osteoid (orange) and bone marrow. Primary hyperoxaluria results in increased excretion of calcium oxalate, with the formation of oxalate stones being common. This occurs due to the failure of the kidneys to clear calcium oxalate into urine. The calcium oxalate crystals are therefore deposited abnormally in the bone marrow forming radial, rosette-type clusters. Calcium oxalate is the main component of kidney stones. Oxalosis is a rare inborn error of metabolism and is a systemic (widespread) disease in the body. Oxalosis of bone is accompanied by calcification of joints, weakened bone