Soil plays a crucial role in ecosystem functioning, e.g., soil minerals provide important provisioning and regulating ecosystem services. The determination of soil mineral composition can help to link geochemical processes to underlying bedrock and surficial geology, however analysing quantitative soil mineralogy by X-ray diffraction can be expensive. This study used data from the North American Soil Geochemical Landscapes Project sampled at sites (n = 560) across Canada; exploratory analysis of major elements from the C-horizon, < 2 mm size fraction, was carried out to determine whether geochemical data can infer site-specific qualitative soil minerals. Results for the raw geochemical data indicated relative variability of major elements across Canadian provinces with noticeable differences for silica and calcium. Geochemical data are compositional, and as such their statistical assessment is subject to the problem of closure. In the current study, all raw geochemical data were centred log-ratio-transformed prior to statistical analysis to overcome closure. Graphical measures indicated skewed element data prior to centred log-ratio transformation, which produced a more symmetric distribution. Correlations between elements suggested tentative soil mineral composition, such as silica and aluminum from aluminosilicates minerals. Principal component analysis of transformed geochemical data revealed three distinct groups of calcium, magnesium; iron, titanium, manganese; and aluminum, potassium, silica, sodium, while phosphorus had smaller relative variability independent of these groups. The interpretation of these groups was based on soil minerals and identified as carbonates, silicates, and weathered secondary oxides. These minerals corresponded geospatially

Weathering of soil minerals provides base cations that buffer against acidity, and nutrients that support plant growth. In general, direct observations of soil minerals are rare; however, their abundance can be determined indirectly through soil geochemistry using normative-calculation procedures. This study compiled a data set of major oxide content from published and archived soil geochemical observations for 1170 sites across Canada (averaged over the soil profile [A, B, and C horizons], weighted by depth and bulk density to a maximum depth of 50 cm). Quantitative soil mineralogy (wt%) was systematically determined at each site using the normative method, ‘Analysis to Mineralogy’ (A2M); the efficacy of the approach was evaluated by comparison to X-ray Diffraction (XRD) mineralogy available for a subset of the study sites. At these sites, predicted A2M mineralogy was significantly related to estimated XRD, showing a strong linear relationship for plagioclase, quartz, and K-feldspar, and a moderate linear relationship for chlorite and muscovite. Further, the predicted A2M plagioclase content was almost identical to the estimated XRD soil mineralogy, showing no statistical difference. The Canada-wide predicted quantitative soil mineralogy was consistent with the underlying bedrock geology, such as in north-western Saskatchewan and north-eastern Alberta, which had high amounts of quartz due to the Western Canadian Sedimentary Basin. Other soil minerals (plagioclase, potassium feldspar, chlorite, and muscovite) varied greatly in response to changing bedrock geology across Canada. Normative approaches, such as A2M, provide a reliable approach for national-scale determination of quantitative soil mineralogy, which is essential for the assessment of soil weathering rates.