Chromium geochemistry in serpentinized ultramafic rocks and serpentine soils from the Franciscan complex of California

TLDR: Chamberland et al. as mentioned in this paper found that chromium concentrations in serpentine soil profiles fluctuate between 1,725 to 4,760 mg kg−1 and do not correspond to variations in soil pH, organic carbon, or electrical conductivity.

Abstract: Weathering of ultramafic rocks and serpentinites in the Franciscan Complex of California produces serpentine soils containing high concentrations of Cr as well as other potentially toxic elements including Ni, Co, and Mn. Chromium concentrations in serpentine soils from Jasper Ridge Biological Preserve in the Central Coast Range are as high as 4,760 mg kg−1, nearly three times greater than the serpentinite protolith (∼1800 mg kg−1). Chromium-containing minerals within the bedrock include chlorite (∼0.3 Cr wt. %), enstatite (∼0.4 Cr wt. %), augite (∼0.7 Cr wt. %), chromite (∼10.8 Cr wt. %), magnetite (8.2-10.3 Cr wt. %), and an ultra fine-grained mixture of spinel and a silicate phase containing ∼13.3 Cr weight percent. Chromium concentrations in serpentine soil profiles fluctuate between 1,725 to 4,760 mg kg−1 and do not correspond to variations in soil pH, organic carbon, or electrical conductivity. The enrichment and variability of soil Cr is directly related to the modal abundance and weathering of chromite, Cr-magnetite, and the spinel-silicate mixture. By comparison, Cr silicates account for