PMID- 33819749
OWN - NLM
STAT- PubMed-not-MEDLINE
LR  - 20210419
IS  - 1873-3557 (Electronic)
IS  - 1386-1425 (Linking)
VI  - 255
DP  - 2021 Jul 5
TI  - Compositional and spectrochemical analyses of Cr-spinels in the Sittampundi 
      Anorthosite Complex, Southern India: Implications for remote observation of 
      spinels on the Moon.
PG  - 119677
LID - S1386-1425(21)00253-5 [pii]
LID - 10.1016/j.saa.2021.119677 [doi]
AB  - The spectroscopic techniques such as Laser Raman, Fourier Transform Infrared 
      (FTIR), and hyperspectral have been used widely to understand the mineral 
      chemistry and crystal structure and identify the functional phases and organic 
      molecules in geological materials on Earth and other planetary bodies. The 
      present study used these spectroscopic techniques combined with X-ray Diffraction 
      (XRD) and Electron Probe Micro Analysis (EPMA) to understand the 
      spectral-compositional relationships of the Cr-spinel (Chromian spinel) present 
      in chromitite bodies associated with Sittampundi Anorthosite Complex (SAC), 
      southern India. The bands/lenses of Cr-spinel are found as layers (few 
      centimeters to 6 m thick) intercalated with anorthosites and clinopyroxenites of 
      the SAC. The cumulate Cr-spinels of the study area exhibit compositions ranging 
      between Al-chromite and Cr-spinel. Fe-, Al-rich Cr-spinel is a characteristic of 
      the SAC with Cr(2)O(3) content ranging from ~32-37 wt% and Cr# (Cr/[Cr + Al]) in 
      the 0.44 to 0.53 range. The XRD spectra of these Cr-spinels have shown 
      characteristic peaks corresponding to its constituent phases, with the highest 
      peak at 36.11 degrees . The observed longward shift in the Raman A(1g) peak 
      (~705-714 cm(-1)) is likely to be caused by the substitution of Al(3+) in the 
      spinel structure. The Raman A(1g) peak position near 705 cm(-1) in the spectra is 
      attributed to the coexistence of (Mg, Fe) in the tetrahedral site and (Al, Cr) in 
      the octahedral site. The broader and stronger 2 microm band position in the 
      hyperspectral data is at relatively shorter wavelengths than typical Cr-spinels 
      due to enhanced Al content (Al(2)O(3) ~ 25 wt%) in the SAC samples. The 2 microm band 
      position is observed to have a longward shift with increasing Cr(2)O(3) and Cr# 
      abundances and a corresponding shortward shift with enhanced Al(2)O(3) content in 
      Cr-spinels. The linear relationship between the 2 microm band position and Cr/Al 
      abundances indicates that this absorption band is significant in distinguishing 
      Cr-spinels from Al-spinels. Based on spectral and compositional resemblance, Fe- 
      and Al-rich Cr-spinels in SAC are considered as probable terrestrial (functional) 
      analogues for similar lunar spinel compositions given that evidence-based 
      correlation of intricate processes involved in their formation under the lunar 
      and terrestrial conditions. The present study demonstrates the approach of 
      applying spectrochemical characteristics of terrestrial analogue spinels for 
      remote identification of lunar spinels and retrieving their compositional ranges 
      from the spectral reflectance parameters.
CI  - Copyright (c) 2021 Elsevier B.V. All rights reserved.
FAU - Thesniya, P M
AU  - Thesniya PM
AD  - Department of Earth and Space Sciences, Indian Institute of Space Science and 
      Technology (IIST), Thiruvananthapuram 695 547, India.
FAU - Saranya, R
AU  - Saranya R
AD  - Department of Geology, University of Kerala, Thiruvananthapuram 695 581, India.
FAU - Rajesh, V J
AU  - Rajesh VJ
AD  - Department of Earth and Space Sciences, Indian Institute of Space Science and 
      Technology (IIST), Thiruvananthapuram 695 547, India. Electronic address: 
      rajeshvj@iist.ac.in.
LA  - eng
PT  - Journal Article
DEP - 20210309
PL  - England
TA  - Spectrochim Acta A Mol Biomol Spectrosc
JT  - Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy
JID - 9602533
SB  - IM
OTO - NOTNLM
OT  - Chemical and spectral analyses
OT  - Cr-spinel
OT  - Lunar spinels
OT  - Sittampundi Anorthosite Complex
OT  - Southern India
OT  - Terrestrial analogue
COIS- Declaration of Competing Interest The authors declare that they have no known 
      competing financial interests or personal relationships that could have appeared 
      to influence the work reported in this paper.
EDAT- 2021/04/06 06:00
MHDA- 2021/04/06 06:01
CRDT- 2021/04/05 20:15
PHST- 2020/07/13 00:00 [received]
PHST- 2021/02/25 00:00 [revised]
PHST- 2021/03/01 00:00 [accepted]
PHST- 2021/04/06 06:00 [pubmed]
PHST- 2021/04/06 06:01 [medline]
PHST- 2021/04/05 20:15 [entrez]
AID - S1386-1425(21)00253-5 [pii]
AID - 10.1016/j.saa.2021.119677 [doi]
PST - ppublish
SO  - Spectrochim Acta A Mol Biomol Spectrosc. 2021 Jul 5;255:119677. doi: 
      10.1016/j.saa.2021.119677. Epub 2021 Mar 9.