Spectral reflectance properties of carbonaceous chondrites: 6. CV chondrites

Abstract

Multiple reflectance spectra of 11 CV chondrites have been measured to determine spectral–compositional relationships for this meteorite class and to aid the search for CV parent bodies. The reflectance of CV chondrite spectra is variable, ranging from ∼5% to 13% at 0.56μm, and ∼5% to 15% at the 0.7μm region local reflectance maximum. Overall slopes range from slightly blue to red for powders, while slab spectra are strongly blue-sloped. With increasing average grain size and/or removal of the finest fraction, CV spectra generally become more blue-sloped. CV spectra are characterized by ubiquitous absorption features in the 1 and 2μm regions. The 1μm region is usually characterized by a band centered near 1.05–1.08μm and a band or shoulder near 1.3μm that are characteristic of Fe-rich olivine. Band depths in the 1μm region for powdered CVs and slabs range from ∼1% to 10%. The 2μm region is characterized by a region of broad absorption that extends beyond 2μm and usually includes band minima near 1.95 and 2.1μm; these features are characteristic of Fe2+-bearing spinel. The sample suite is not comprehensive enough to firmly establish whether spectral differences exist between CVR, CVOxA, and CVOxB subclasses, or as a function of metamorphic grade. However, we believe that the mineralogic and petrologic differences that exist between these classes, and with varying petrologic subtype (CV3.0–>3.7), may not be significant enough to result in measurable spectral differences that exceed spectral variations within a subgroup, within an individual meteorite, or as a function of grain size. Terrestrial weathering seems to affect CV spectra most noticeably in the visible region, resulting in more red-sloped spectra for finds as compared to falls. The search for CV parent bodies should focus on the detection of olivine and spinel absorption bands, specifically absorption features near 1.05, 1.3, 1.95, and 2.1μm, as these are the most commonly seen spectral features of CV chondrites.