Desert varnish

Most of the desert pavement stones are covered with a brown-black and shiny crust. When the stones are composed of limestone, the dark crust contrasts strongly with the much lighter inside color exposed on fracture surfaces. The crust forms on various stones, both sedimentary and igneous and is also known under the name of desert varnish , or desert patina . The varnish is less common on non-resistant rocks such as a soft limestone. These, apparently, disintegrate before the crust has time to develop. 

Abrasion and erosion. The dust-loaded wind has an erosive action and contributes to a physical disintegration of rock surfaces or to a polishing of the components of the desert pavement, giving them a characteristic patina desert varnish) and shape (ventifacts). 

Allen, C. C. (1978). Desert varnish of the Sonoran Desert - optical and electron probe microanalysis. Journal of Geology, 86, 743-52. 

Elvidge, C. D. (1982). Reexamination of the rate of desert varnish formation reported south of Barston, California. Earth Surface Processes andLandforms, 7, 345-8. 

Rock varnish (often called desert varnish when seen in drylands) is a paper-thin mixture of about two-thirds clay minerals cemented to the host rock by typically one-fifth manganese and iron oxyhydroxides. Upon examination with secondary and backscattered electron microscopy, the accretionary nature of rock varnish becomes obvious, as does its basic layered texture imposed by clay minerals (Dorn and Oberlander, 1982). Manganese enhancement, two orders of magnitude above crustal values, remains the geochemical anomaly of rock varnish and a key to understanding its genesis. 

Desert varnish occurs in deserts and not elsewhere, and this distribution somehow relates to mode of formation... 

Bao, H., Michalski, G.M. Thiemens, M.H. (2001) Sulfate oxygen-17 anomalies in desert varnishes. Geochimica et Cosmochimica Acta 65, 2029-2036. 

Borns, D.J., Adams, J.B., Curtiss, B., Farr, B., Palmer, T., Staley, J. Taylor-George, S. (1980) The role of microorganisms in the formation of desert varnish and other rock coatings SEM study. Geological Society of America Abstracts with... 

Cremaschi, M. (1996) The desert varnish in the Messak Sattafet (Fezzan, Libryan Sahara), age, archaeological context and paleo-environmental implication. Geoarchaeology 11, 393-421. 

Diaz, T.A., Bailley, T.L. Orndorff, R.L. (2002) SEM analysis of vertical and lateral variations in desert varnish chemistry from the Lahontan Mountains, Nevada. Geological Society of America Abstracts with Programs, 7-9 May Meeting, http //gsa.confex.com/gsa/2002RM/finalprogram/abstract 33974.htm. 

Dorn, R.L Oberlander, T.M. (1981) Microbial origin of desert varnish. Science 213, 1245-1247. 

Dragovich, D. (1986) Minimum age of some desert varnish near Broken Hill, New South Wales. Search 17, 149-151. 

Engel, C.G. Sharp, R.S. (1958) Chemical data on desert varnish. Geological Society of America Bulletin 69, 487-518. 

Flood, B.E., Allen, C. Longazo, T. (2003) Microbial fossils detected in desert varnish. Astrobiology 2, 608. 

Glasby, G.P., McPherson, J.G., Kohn, B.P., Johnston, J.H., Keys, J.R., Freeman, A.G. Tricker, M.J. (1981) Desert varnish in southern Victoria Land, Antarctica. New Zealand Journal of Geology and Geophysics 24, 389-397. 

Hooke, R.L., Yang, H. Weiblen, P.W. (1969) Desert varnish an electron probe study. Journal of Geology 77, 275-288. 

Hungate, B., Danin, A., Pellerin, N.B., Stemmier, J., Kjellander, P., Adams, J.B. Staley, J.T. (1987) Characterization of manganese-oxidizing (Mnll —> MnlV) bacteria from Negev Desert rock varnish implications in desert varnish formation. Canadian Journal of Microbiology 33, 939-943. 

Kenea, N.H. (2001) Influence of desert varnish on the reflectance of gossans in the context of Landsat TM data, southern Red Sea Hills, Sudan. International Journal of Remote Sensing 22, 1879-1894. 

Lakin, H.W., Hunt, C.B., Davidson, D.F. Odea, U. (1963) Variation in minor-element content of desert varnish. U.S. Geological Survey Professional Paper 475-B, B28-B31. 

Laudermilk, J.D. (1931) On the origin of desert varnish. American Journal of Science 21, 51-66. 

Lee, M.R. Bland, P.A. (2003) Dating climatic change in hot deserts using desert varnish on meteorite finds. Earth and Planetary Science Letters 206, 187-198. 

Mancinelli, R.L., Bishop, J.L. De, S. (2002) Magnetite in desert varnish and applications to rock varnish on Mars. Lunar and Planetary Science 33, 1046. pdf. 

Moore, C.B. Elvidge, C.D. (1982) Desert varnish. In Bender, G.L. (Ed.) Reference handbook on the deserts of North America. Westport Greenwood Press, pp. 527-536. 

Palmer, F.E., Staley, J.T., Murray, R.G.E., Counsell, T. Adams, J.B. (1985) Identification of manganese-oxidizing bacteria from desert varnish. Geomicrobiol-ogy Journal 4, 343-360. 

Patyk-Kara, N.G., Gorelikova, N.V., Plakht, J., Nechelyustov, G.N. Chizhova, I.A. (1997) Desert varnish as an indicator of the age of Quaternary formations (Makhtesh Ramon Depression, Central Negev). Transactions (Doklady) of the Russian Academy of Sciences/Earth Science Sections 353A, 348-351. 

Perry, R.S. Kolb, V.M. (2003) Biological and organic constituents of desert varnish Review and new hypotheses. In Hoover, R.B. Rozanov, A.Y. (Eds) Instruments, Methods, and Missions for Astrobiology VII. Bellingham, WA Society of Photo-Optical Instrumentation Engineers, pp. 202-217. 

Perry, R.S., Engel, M., Botta, O. Staley, J.T. (2003) Amino acid analyses of desert varnish from the Sonoran and Mojave deserts. Geomicrobiology Journal 20, 427-438. 

Potter, R.M. (1979) The tetravalent manganese oxides clarification of their structural variations and relationships and characterization of their occurrence in the terrestrial weathering environment as desert varnish and other manganese oxides. PhD dissertation, Earth and Planetary Science, California Institute of Technology, Pasadena. 

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