Fig 1.
Representative x-ray patterns from marine bryozoan skeletal carbonates.
X-axis is the angle of the exiting x-ray beam in degrees 2 theta (°2θ), which varies depending on the crystal structure of the material it encounters. Y-axis is peak height in “counts” which is different for every run and not relevant – it is the relative peak height that indicates proportions of minerals present. Measured peaks are: Aragonite 1 (26.2 °2θ); A2 - Aragonite 2 (27.2 °2θ); C1 - Low-Mg Calcite (29.3 °2θ); C2 - High-Mg Calcite (29.7 °2θ). A small unmeasured calcite peak sometimes appears at 27.5 °2θ. The internal standard of Halite is at 31.7 °2θ.
Table 1.
Carbonate mineral composition of 17 standard mixtures used to calibrate trimineralic analysis.
Fig 2.
Ternary diagram showing seventeen standards used to calibrate tri-mineralic analysis, consisting of mixtures of Aragonite, high-Mg calcite and low-Mg calcite, in percent by weight.
Table 2.
Locality data for specimens of New Zealand black-footed pāua Haliotis iris used in this study.
Fig 3.
Pāua shell with areas selected for XRD analysis highlighted, including: axial length (solid white line), and radial length (top dashed line), and where shells were sectioned (along the dashed lines).
The spire (OLD), middle (MID), and edge (NEW) sections were powdered for XRD analysis.
Fig 4.
A. Estimated weight fractions are aligned with actual weight fractions for all three minerals (R2 > 0.99 for all minerals; estimated slopes = 1.01, 1.01, 1.00 for Aragonite, Low-Mg Calcite (LMC) and High-Mg Calcite (HMC)). B. Comparison of calibration from [4] using standard bimineral PHR correlation and the calibration from this study shows the improvement from this study for analysing calcite subcompositions.
Fig 5.
The mean absolute error across all samples with non-zero weight fractions was 2%.
However, the error depends on the weight fraction, and is highest when the weight fraction equals 50% (for a given peak height). Error also depends on the sum of peak heights, decreasing as the sum increases (not shown). Minerals: Aragonite, Low-Mg Calcite (LMC) and High-Mg Calcite (HMC).
Fig 6.
Precision for repeated measurements of a single trimineral sample were similar whether the sample remained in the instrument, or was removed and replaced by an operator (with no change to the smear mount).
Measurements of different samples from the same underlying mixture showed greater variability due to random assortment.
Fig 7.
Skeletal carbonate mineralogy of 252 samples from 28 individual specimens of Haliotis iris, mostly from southern New Zealand.
All samples contain aragonite, 96% contain low-Mg calcite, and 39% contain both high-Mg calcite and low-Mg calcite.
Fig 8.
Skeletal carbonate mineralogy of individual specimens of Haliotis iris from Kaikoura (left) and Karitane (right).
Specimen names indicate species (HI) – location (KK or SNZ) – shell length in mm (from 22 to 135 mm) – part of the shell sampled (spire, middle, edge, see Fig 3) – and replicate (n = 3).
Table 3.
Skeletal carbonate mineralogy of abalone in the genus Haliotis Linnaeus, 1758. Of the c. 60 species, 18 have been studied.