Chromium isotope

Chromium in the crystalline form is a steel-gray, lustrous, hard metal characterized by an atomic weight of 51.996, an atomic number of 24, a density of 7.14 g/cm3, a melting point of 1857°C, and a boiling point of 2672 C. Four chromium isotopes occur naturally Cr-50 (4.3%), -52 (83.8%), -53 (9.6%), and -54 (2.4%), and seven are man-made. Elemental chromium is very stable but is not usually found pure in nature. Chromium can exist in oxidation states ranging from -2 to +6, but is most frequently found in the environment in the trivalent (+3) and hexavalent (+6) oxidation states. The +3 and +6 forms are the most important because the +2, +4, and +5 forms are unstable and are rapidly converted to +3, which in turn is oxidized to +6 (Towill et al. 1978 Langard and Norseth 1979 Ecological Analysts 1981 USPHS 1993). 

Chromium iron manganese brown spinel, formula and DCMA number, 7 348t Chromium iron nickel black spinel, formula and DCMA number, 7 348t Chromium isotopes, 6 476 Chromium magnesium oxide, 5 583 Chromium manganese zinc brown spinel, formula and DCMA number, 7 348t Chromium-nickel alloys, 77 100-101 Chromium-nickel-iron alloys, 17 102-103 Chromium-nickel stainless steels, 15 563 Chromium niobium titanium buff rutile, formula and DCMA number, 7 347t Chromium(III) nitrate, 6 533 Chromium nitride, 4 668... 

Schauble EA, Rossman GR, Taylor Jr. HP (2001) Theoretical estimates of equilibrium Fe-isotope fractionations from vibrational spectroscopy. Geochim Cosmochim Acta 65 2487-2497 Schauble EA, Rossman GR, Taylor Jr. HP (2003) Theoretical estimates of equilibrium chlorine-isotope fractionations. Geochim Cosmochim Acta 67 3267-3281 Schauble EA, Rossman GR, Taylor Jr. HP (2004) Theoretical estimates of equilibriimi chromium-isotope fractionations. Chem Geol, in press. 

Birck JL, Allegre CJ (1984) Chromium isotopic anomalies in Allende refractory inclusions. Geophys Res Lett 11 943-946... 

Birck JL, Allegre CJ (1988) Manganese chromium isotope systematics and development of the early solar system. Nature 331 579-584... 

Meyer BS (1994) The r-, s-,and p-processes in nucleosynthesis. Annu Rev Astronom Astrophys 32 153-190 Mostefaoui S, Lugmair GW, Hoppe P, El Goresy A (2003) Evidence for live iron-60 in Semarkona and Chervony Kut a nanosims study. Lunar Planet Sci XXXIV 1585 Murthy VR, Sandoval P (1965) Chromium isotopes in meteorites. J Geophys Res 70 4379-4382 Nicolussi GK, Davis AM, Pellin MJ, Lewis RS, Clayton RN, Amari S (1997) s-Process zirconium in presolar silicon carbide grains. Science 277 1281-1283... 

Papanastassiou DA (1986) Chromium isotopic anomalies in the Allende meteorite. Astrophys J 308 L27-L30 Papanastassiou DA, Wasserburg GJ (1969) Initial strontium isotopic abundances and the resolution of small time differences in the formation of planetary objects. Earth Planet Sci Lett 5 361-376 Papanastassiou DA, Wasserburg GJ (1978) Strontium isotopic anomalies in the Allende meteorite. Geophys Res Lett 5 595-598... 

Rolfs CE, Rodney WS (1988) Cauldrons in the cosmos. University of Chicago Press, Chicago Rotaru M, Birck JL, Allegre CJ (1992) Clues to early solar system history from chromium isotopes in carbonaceous chondrites. Nature 358 465-470... 

Mass-Dependent Fractionation of Selenium and Chromium Isotopes in Low-Temperature Environments... 

CHROMIUM ISOTOPE SYSTEMATICS Equilibrium isotope fractionation... 

Beaudoin G, Taylor BE, Rumble III D, Thiemens M (1994) Variations in the sulfur isotope composition of troilite from the Canon Diablo iron meteorite. Geochim Cosmochim Acta 58 4253-4255 Birck JL, Allegre CJ (1988) Manganese-chromium isotope systematics and the development of the early solar system. Nature 331(6157) 579-584... 

Lee T, Tera F (1986) The meteoritic chromium isotopic composition and limits for radioactive Mn in the early solar system. Geochim Cosmochim Acta 50(2) 199-206 Lemly AD (1985) Toxicology of selenium in a freshwater reservoir Implications for environmental hazard evaluation and safety. Ecotoxicol Environ Saf 10 314-338 Lemly AD (1998) Pathology of Selenium Poisoning in Fish. In Environmental Chemistry of Selenium. 

Schauble E, Rossman GR, Taylor HP (in press) Theoretical estimates of equilibrium chromium-isotope fractionations. Chem Geol... 

EUiott T, Jeff coate AB, Bouman C (2004) The terrestrial Li isotope cycle light-weight constraints on mantle convection. Earth Planet Sci Lett 220 231-245 Ellis AS, Johnson TM, Bullen TD (2002) Chromium isotopes and the fate of hexavalent chromium in the environment. Science 295 2060-2062... 

Izbicki JA, BaU JW, Bullen TD, Sutley S J (2008) Chromium, chromium isotopes and selected trace elements. Western Mojave Desert, USA, Appl Geochemistry 23 1325-1352 Jaffres JB, Shields GA, Wallmann K (2007) The oxygen isotope evolution of seawater a critical review of a long-standing controversy and an improved geological water cycle model for the past 3,4 billion years. Earth Sci Rev 83 83-122... 

Volatile metal chelates are also useful in determining isotope ratios of geological interest, e.g., the Zr/Hf ratio (197). This method proved invaluable as a microtechnique for chromium isotope analysis of lunar samples from the Apollo program (198). 

The Mn- Cr system can be studied by TIMS, ICPMS, and SIMS techniques. For TIMS and ICPMS work, bulk samples or mineral separates are dissolved and the solutions are passed through ion-exchange columns to produce clean solutions of manganese and chromium. For minerals with high Mn/Cr ratios SIMS can obtain isotopic data while retaining the petrographic context of the measurements. The chromium isotopic compositions may have to be corrected for small additions of chromium from spallation reactions induced by cosmic rays. This is particularly important in iron-rich meteorites. 

Birck, J. L. and Lugmair, G. W. (1988) Nickel and chromium isotopes in Allende inclusions. Earth and Planetary Science Letters, 90, 131-143. 

Chromium speciation has also been successfully achieved by using SFC [99]. Two p-ketonate chromium compounds and an organochromium dimer were separated initially, using C02 as the mobile phase. However, as a result of an isobaric interference at m/z 52 (the major chromium isotope) from the formation of 40Ar12C+, nitrous oxide was used instead. 

Nyquist L., Bansal B., Wiesmann H., and Shih C.-Y. (1994) Neodymium, strontium, and chromium isotopic studies of the LEW86010 and Angra dos Reis meteorites and the chronology of the angrite parent body. Meteoritics 29, 872-885. 

Papanastassiou D. A. (1986) Chromium isotopic anomalies in the AUende meteorite. Astrophys. J. 308, L27-L30. 

Frei, R. and Rosing, M.T., 2005. Search for traces of the late heavy bombardment on Earth - results from high precision chromium isotopes. Earth Planet. Sci. Lett., 236, 28—40. 

---