Soil Under a Microscope - Slide 60

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Special Features: Gibbsite

Gibbsite is a mineral found in highly weathered soils such as Ultisols and Oxisols and under special circumstances, in Inceptisols and Andisols. The aluminum oxyhydrate (AlO-OH3) crystallizes when soil pH > than about 5.5 and the most common mineral is gibbsite. Boehmite, the mono-hydrate is rare. (a) shows a gibbsitic nodule (X50) with whitish gibbsite crystals and with well defined crystals at X 5,000 (b). (c) is an insitu alteration of feldspar directly to large gibbiste crystals (d) x5,000.