Abstract
Both palygorskite and sepiolite occur as sheets in tension fracture zones, fault zones, and caves in rock strata, as well as forming strata in alluvial terraces. The sheets of fibrous clays were commonly named mountain leather or mountain cork. The fibrous clays occur in geologic host rock systems of Paleozoic and Mesozoic ages as well as Quaternary age. The analyzed palygorskites represent a continuous series with Al
2O
3 contents ranging from 16.3 wt.% to 4.8 wt.% and (110) XRD peaks from 10.30 Å to 10.57 Å. When less than about 8 wt.% Al
2O
3 is present secondary NIR Mg related OH bands may be observed along with the palygorskite spectra. The analyzed sepiolites have (110) XRD
d-values ranging from 12.03 Å to 12.26 Å. The latter is an Fe-sepiolite (xylotile). DTA analyses show that the palygorskite exotherm temperatures form a linear function with the Al
2O
3 contents, from 1045 °C at 16.3 wt.% to 880 °C at 4.8 wt.% Al
2O
3. The fibrous clays can readily adsorb considerable amounts of metals, such as Pb, As, and Cd. The amounts held can be used for determining whether the clays are classified as hazardous materials, on the basis of U.S. EPA and California State standards.