Abstract-The instability of palygorskite and sepiolite under soil conditions was investigated to determine if these fibrous minerals transform directly to smectite under laboratory conditions. The treatment of 100 mg (0.12 mmole) of palygorskite with 1 mmole of NaOH solution (17 ml) at 150~ for 24 hr yielded a smectite. Analcime and smectite were formed when -> 3 mmole of NaOH was used. The addition of -<6 mmole NaOH to sepiolite destroyed it gradually. On addition of ->8 mmole NaOH, sepiolite altered to an X-ray amorphous material. In the presence of A1 and Si, however, it transformed to smectite and analcime. Transmission electron microscopy, cation-exchange capacity, and X-ray powder diffraction studies of the products suggest that alteration was (1) via solution, or (2) by a structural reorganization wherein the basic 2:1 silicate structural units were unchanged.

No abstract

Abstract--The occurrence of palygorskite in some Tertiary sediments in eastern Saudi Arabia was studied. Mineralogical and chemical analyses were made of samples from two sections several meters thick from the Umm er Radhuma and Dammam Formations of Paleocene and Eocene periods, respectively. Layers of shales were observed within the sections of the dolomitic-calcitic limestone of the Umm er Radhuma Formation and of the dolomitic limestone of the Dammam Formation. After treatment for carbonate removal the shales consisted of more than 95% clay-size particles, most of which were <0.2-#m in size. Palygorskite was the main constituent of some of the shales, with minor amounts of gypsum, soluble salts, and carbonates. The association of gypsum and other salts with palygorskite in the shale suggests that palygorskite formed in closed-basin environments. The presence of palygorskite and the absence of other minerals in the clay fraction of the limestones also suggests that the palygorskite formed under marine conditions.

Rock samples representing different soil parent materials from the Jurassic, Cretaceous and Tertiary periods in eastern Saudi Arabia were investigated for their mineralogical and chemical properties. Samples from five soil profiles found on these rocks also were studied. Palygorskite was found to be the dominant mineral in the clay fraction of the Tertiary and upper Cretaceous sediments. Some shales of Tertiary origin contained mainly palygorskite with minor amounts of gypsum and soluble salts. Palygorskite was not found in any sediments of the early lower Cretaceous and Jurassic periods, and kaolinite was the dominant mineral in the clay fraction of those sediments. Soils associated with Jurassic limestone near the Riyadh area also showed a predominance of kaolinite in their clay fractions. However, the clay fractions of the soils found on Tertiary sediments in the eastern part of the country were dominated by palygorskite. The presence of palygorskite in the soils paralleled its presence in the parent materials or the rocks exposed in the area. Eolian transport of palygorskite was found to be a factor for the occurrence of palygorskite in the soils. Thus, the major portion of the soil palygorskite probably originated from the Tertiary sediments in eastern Saudi Arabia.

No abstract