# Raman spectroscopic analysis of carbonates on a CY-type carbonaceous chondrite Yamato 980115: unexpectedly abundant terrestrial weathering products

## TL;DR

This study used Raman spectroscopy to find that most carbonates in a meteorite are nesquehonite, a weathering product from Earth, not expected in space.

## Contribution

The study reveals an unexpected abundance of terrestrial weathering products in a carbonaceous chondrite using Raman spectroscopy.

## Key findings

- 60 out of 63 carbonate grains on Y 980115 were identified as nesquehonite.
- No dolomite was found despite initial expectations.
- Nesquehonite is a typical terrestrial weathering product, suggesting significant Earth influence.

## Abstract

This study presents Raman spectra of carbonates on a carbonaceous chondrite, Yamato (Y) 980115. Y 980115 is an Antarctic meteorite and is originally classified as CI1-type. Since CI1-type meteorites are expected to record information of aqueous alteration of carbonaceous matters in the primitive solar photosphere or planetesimals, extensive studies have been performed. Among a variety of minerals on meteorites, carbonates are one of environment indicators because its cation composition depends on thermochemical properties of the aqueous solution when they were precipitated. Although the minerals on meteorites are usually identified by elemental composition analysis techniques such as backscattered electron imaging, these techniques have a drawback that they lack information of crystal structures so that it is difficult to distinguish some minerals such as ordered or disordered dolomite (CaMg(CO3)2) and a mixture of calcite (CaCO3) and magnesite (MgCO3). The present study employed Raman spectroscopy as a complementary technique to the elemental composition analysis. As a result, surprisingly, while the Mg-bearing carbonates on Y 980115 were expected mainly to be dolomite, the Raman spectra revealed that they are indeed nesquehonite (Mg(HCO3)(OH)·2H2O), which is a typical terrestrial weathering product for Antarctic meteorites. Among 63 carbonate grains found on Y 980115, 60 and 3 grains were assigned to nesquehonite and calcite, respectively, and no dolomite was found. This result indicates that there are unexpectedly abundant terrestrial weathering products for carbonates found on Y 980115.