Origin and characteristics of Cr-smectite from Suweileh area, Jordan

• A new discovered locality of Cr-smectite in Suweileh Jordan.
• The Cr-smectite is characterized mineralogically and chemically.
• Combusted bituminous marl was the source of Cr3 +.
• Secondary Cr-rich smectite precipitates along weakness zones.

Unique green earthy clay occurs as thin layers along bedding planes, and in cavities and fractures in Suweileh area, Jordan. The collected green earthy samples were subjected to microscopic, chemical, thermal, infrared, XRD, SEM and EDX analyses. The source of Cr3 + is the varicolored marble of upper Cretaceous age in Suweileh area (dominated by recrystalline calcite and apatite). These rocks are equivalent to the varicolored marble in central (Daba Siwaqa) and north Jordan (Maqarin).Currently, hyperalkaline circulating waters (pH ~ 12.7) are active in Maqarin area, north Jordan. Combustion of the organic matter in the bituminous phosphatic marl has accelerated the leaching of Cr3 + among other redox sensitive trace elements. Cr-smectite has precipitated from the alkaline circulating water enriched with Cr3 +. The uninterrupted continuous flaky growth of the smectite suggests its chemical origin. Smectites are expected to be a sink of alteration products in the late stage evolution of a high pH plume. Chromium substitution for aluminum in a pre-existing smectite is also indicated in the same area. The spot chemical analysis of Suweileh smectite has indicated the following structural formula: Ca0.30Na0.23(Al0.47Cr0.63Fe0.13Mg0.66Zn0.06Ti0.03)(Si3.88Al0.12)O10(OH)2. The formula indicates that Cr3 + is immobilized in the octahedral layer of smectite.

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