An apparatus for detecting one or more organic compounds in a gem, comprising a probe for irradiating a surface of a gem with near infrared radiation, to generate internal reflections of the near infrared radiation within the gem, wherein the internal reflections are substantially diffuse; a near infrared radiation transmissive conduit for collecting internally reflected near infrared radiation from a surface of the gem, the internally reflected energy comprising components which are diffuse; a spectrometer for analyzing the collected internally reflected diffuse near infrared radiation from the gem, to determine if spectral characteristics indicative of at least one organic compound are present in the gem.