Organic compounds associated with thin carbonaceous films on crack surfaces have been detected by thermal-desorption photoionization mass spectrometry in large single crystals of olivine from San Carlos, Arizona and Hualalai Volcano, Hawaii. Alkalis, silicon, aluminum and halogens are also present in the 3-4 nm thick carbonaceous films. The organics probably were not derived from the upper mantle or lower crust or from environmental biogenic contamination after eruption and cooling. It is likely that the carbonaceous films and organics were deposited or formed on crack surfaces created during eruption and cooling of the host alkali basalts. Whether the organics were produced abiotically by Fischer-Tropsch-like reactions involving volcanic gases and fresh-fractured surfaces where reduced carbon was deposited, or whether the organics represent biogenic material that was assimilated into the magmatic system prior to or during magma ascent, cannot be ascertained at this time due to their low abundance.
