Diffuse reflectance spectroscopy using near infrared and mid infrared radiation is used to detect the presence of organic chemical compounds in gems. Suitably, diffuse reflectance infrared Fourier transformation spectroscopy is employed to detect the presence of organic compounds in gems using mid infrared and near infrared radiation. The apparatus uses an integrating sphere or integrating cylinder with a probe that acts as both a source of near infrared radiation and a detector of reflected diffuse internal energy from the gem. Alternatively, the integrating sphere or integrating cylinder is replaced with a reflective fluid which surrounds the gem and causes total internal reflection.