322 Subsurface Geologic Methods 



angstrom units excites petroleum fluorescence, although the so-called 

 near-ultraviolet, that approximating 3,650 angstrom units, usually excites 

 the brightest response. 



Ultraviolet light can be employed on sands, shales, drill cores, and 

 drillings, as well as soil samples, not only to detect petroleum but also to 

 reveal the presence of other formations or for detecting economically 

 important mineral species. More than 200 minerals and gems fluoresce 

 under ultraviolet light and other exciting radiations.^^ 



As an activator in solids, little is actually known about the role 

 petroleum plays. In friable soils and earths, it is probable that the oil 

 exists in physical combination, e.g., sorptively bonded, with these mater- 

 ials. Traces of petroleum may be found disseminated throughout a crystal- 

 line mineral, producing a fluorescent effect that may be typical of the 

 oil or of the mineral and oil combined. Texas localities yield large crystals 

 of calcite containing oil, and this is responsible for a fluorescence independ- 

 ent of manganese or rare-earths activation. 



Oil shales provide interesting fluorescences under ultraviolet light. 

 Common shales ("blaes") appear a very dark brown in the massive state, 

 whereas the color may be absent in the powdered shale. With a kerogen 

 shale, a rich chocolate-brown may be observed in both lump and powdered 

 forms. Torbanite can be distinguished from cannel by the bright yellow 

 streaks on a brown background.^® ^^ ^^ Useful indications are obtained as 

 to the origin, preparation, and process of cleaning of Esthonian and Man- 

 churian shale oils; individual fractions can be graded according to boiling 

 points, all by fluorescent response. ^^ 



There is a good deal of information available on the fluorochemistry 

 of substances related to petroleum.-^ -^ Asphalts, coal tars, bitumens, coals, 

 and sundry organic minerals not only fluoresce, but the fluorescence can 

 often be seen at great dilutions. The origin of such materials can be 

 empirically identified by the response; a trace of coal-tar pitch, for ex- 

 ample, shows in asphalt by its greenish-blue emission when present at a 

 ratio of 1:50,000.22 



Petroleum oils and most refined petroleum products, whether liquid 

 or solid, fluoresce at great dilutions in various liquid solvents. The sol- 

 vents usually preferred include benzene, hexane, ethyl ether, carbon 

 tetrachloride, various straight-chain hydrocarbons, and the like. The pres- 

 ence of a nitro group or of chlorine in the solvents generally acts to dim- 

 inish the intensity of the fluorescence. 



The detection threshold varies according to the method employed. 



^^De Ment, Jack, Ultra-Violet Prod., Inc., Bull., no. 2, p. 1, 1944; Oil and Gas Jour., vol. 44, 

 pp. 75-80. 1945; Handbook of Fluorescent Gems and Minerals, Portland, Ore., Mineralogist Publish- 

 ing Co., 1949. 



" Radley, G., and Grant. J., op. cil. 



'' Danckwortt. P., op. cit. 



'^ Haitinger. M.. op. cit. 



"Wittich, M., Brennstoff-Chemie, Heft 19, 1927. 



^^ Pringsheim, P., and Vogel, M., op. cit. 



^ De Ment, Jack, op. cit., 1945. 



22Teuscher, W. Chem. Fabrik, Band 53, 1930; Band 54, 1930. 



