Trimineralic abalone shells (Haliotis iris Gmelin, 1791) and X-ray diffractometry: A Bayesian calibration model for...

Area of Science:

• Geochemistry
• Biomineralization
• Analytical Chemistry

Background:

• X-ray diffractometry (XRD) is standard for analyzing carbonate minerals in marine skeletons.
• Abalone shells can contain multiple carbonate minerals, including aragonite, high-Mg calcite, and low-Mg calcite.
• Accurate quantification of these minerals in trimineralic samples is challenging.

Purpose of the Study:

• To develop and validate a novel Bayesian calibration model for analyzing trimineralic biogenic carbonate using XRD.
• To assess the system's accuracy, precision, and sources of error.
• To investigate mineralogical variations in the New Zealand black-footed pāua (Haliotis iris).

Main Methods:

• Development of a Bayesian calibration model extending the Reference Intensity Ratio method.
• Accommodation of heteroskedastic noise in XRD data analysis.
• Validation using biomineral standards and application to Haliotis iris specimens.

Main Results:

• The new XRD analysis system accurately quantifies relative proportions of aragonite, high-Mg calcite, and low-Mg calcite.
• Mineralogical analysis of Haliotis iris revealed the presence of all three carbonates in many specimens, particularly from Kaikoura.
• Older pāua shell sections showed decreased calcite content, likely due to wear.

Conclusions:

• The developed Bayesian method provides a precise tool for analyzing complex biogenic carbonates.
• The study confirms the unusual trimineralic nature of some Haliotis iris shells.
• This research offers the first detailed uncertainty and precision analysis for XRD in skeletal carbonate mineralogy.