The mineralogy of ordinary chondrites and implications for asteroid spectrophotometry

Graves Nunataks 95209: A snapshot of metal segregation and core formation

“…5B). Feldspar abundances are similar (9.6-16.6% of total silicates in GRA 95209) to those in H chondrites (12.8%;McSween et al, 1991). GRA 95209 is markedly depleted in troilite relative to metal (troilite/(troilite + metal) = 0.4-13.5%).…”

A coordinated spectral, mineralogical, and compositional study of ordinary chondrites

“…The Burbine et al (2003) calibration yields ordinary chondrite ol/(ol + px) ratios that fall within the same general range of ol/ (ol + px) ratios measured from normative mineral abundances of ordinary chondrites (McSween et al, 1991). However, there are systematic differences between the two data sets.…”

“…As a result, the oxides associated with pigeonite (primarily FeO and MgO) are incorrectly allocated in the CIPW norm calculation. A comparison of normative mineralogies (McSween et al, 1991), electron microprobe-measured chondrite abundances (Gastineau-Lyons et al, 2002), and our XRD-measured abundances suggests that these oxides are incorrectly allocated to olivine, resulting in overestimated normative olivine abundances and lower than expected high-Ca pyroxene (Dunn et al, 2010a). Due to the absence of pigeonite from the set of ideal normative minerals, ratios of ol/(ol + px) calculated using normative abundances (Burbine et al, 2003) are not representative of ordinary chondrite mineralogies and do not provide the most accurate calibration for spectral abundances.…”

“…XRD-measured abundances of olivine, orthopyroxene, clinopyroxene, and pigeonite (reported as ol/(ol + px)) are presented in Table 2, along with ol/(ol + px) ratios calculated from CIPW norms (McSween et al, 1991) using the bulk chemical analyses of Jarosewich (1990Jarosewich ( , 2006. The average error associated with XRDmeasured ol/(ol + px) ratios is 0.03, which is based on the uncertainty in determination of olivine and pyroxene abundances (±2 wt.%) (Dunn et al, 2010a).…”

Anatomy of a Partially Differentiated Asteroid: A “NEAR”-Sighted View of Acapulcoites and Lodranites

“…Mafic silicate compositions (olivine, Fa 4.2-11.9 ; orthopyroxene, Fs 6.5-12.6 ) are intermediate between enstatite and H-group ordinary chondrites. The reduced nature of the acapulcoites is also reflected by their orthopyroxene/olivine ratio, which is higher in acapulcoites (∼1.9; Hiroi and Takeda 1991) than in H-group ordinary chondrites (∼0.8; McSween et al 1991). These similarities have led several authors (e.g., Yanai and Kojima 1991) to suggest that acapulcoites are chondritic rocks intermediate between E and H chondrites.…”