Ivory undergo ultraviolet analysis. Mammoth ivory, unlike elephant ivory, can display intrusive brown or blue-green coloured blemishes caused by an iron phosphate, viviante, which shows a spectacular performance under ultra violet light. Ancient ivory acquires unique and beautiful colourations of golden and chocolate browns, orange and occasionally pink, blue and green. The pleasing colour is due to minerals in the soil absorbing into the ivory, which has been buried for thousands of years.