Naturally occurring asbestos (NOA) can be found in serpentinized ultramafic parent material and associated soils, which appear throughout California and Oregon.� These landscapes pose a potential danger to human health if particles are liberated from the soil and inhaled.� The objective of this study was to examine the weathering patterns of NOA minerals in soil horizons and dust across a developmental sequence in serpentinitic landscapes.� We have examined NOA mineral (chrysotile) abundance and location in the soil profiles using x-ray diffraction, polarized light microscopy, and transmission electron microscopy.� We have found that there is a negative relationship between abundance of chrysotile in the solum and weathering intensity.� In soils with a low weathering index (< 30), the abundance of chrysotile bundles in the fine sand, clay, and dust fractions, generally decreased with proximity to the soil surface, while needles increased.� In soils with a moderate weathering index (>30), chrysotile needles and bundles increased with proximity to the soil surface in the fine sand and clay fractions, but decreased in the dust fractions. �The results indicated that during initial stages of development, chrysotile bundles and needles were liberated from parent material through physical and chemical weathering processes.� In the moderately weathered soils, bundles continued to weather further into smaller size fractions, resulting in more needles in the clay fractions.�� In the dust fractions, numerous chrysotile needles were found in the weakly weathered soils, while the moderately weathered soils contained few to no needles.� The A horizons of the moderately weathered soils produced the largest quantities of dust, contained the lowest abundance of chrysotile, pedogenic iron and clay, but also the highest percent carbon.� This indicated that soils containing NOA in intensely weathered environments have a lower potential to release chrysotile needles in dust than soils in mild weathering environments.�

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