Bulk and Detailed Clay (<4 micron) Analysis
    K/T GeoServices, Inc.
        X-ray Diffraction Mineralogy with Impact
 
 
 
 

Home	Sample Preparation Samples submitted for XRD analysis are first disaggregated using a mortar and pestle, weighed, and dispersed in a dilute sodium phosphate solution using a sonic probe.  The samples are next centrifugally size-fractionated into a bulk (>4 microns) and a clay-size (<4 microns ESD) fraction.  The clay suspensions are then decanted and vacuum-deposited on silver metal membrane filters to produce oriented mounts.  Clay mounts are attached to glass slides and exposed to ethylene glycol vapor for a minimum of 24 hours to aid in detection and characterization of expandable clays.  The bulk fractions of each sample are dried and weighed in order to determine weight loss due to removal of clay-size materials, and then pulverized in deionized water using a McCrone micronizing mill.  The resultant powders are disaggregated and packed into aluminum powder mount holders to produce random mounts.
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Analytical Procedures
XRD analyses of the bulk and clay-size fractions of the samples are performed using a  Rigaku or Scintag automated powder diffractometer equipped with a Cu X-ray radiation source (40 Kv, 35 mA) and a solid state or scintillation detector.  The glycol-solvated oriented clay mounts are analyzed over an angular range of 2-50 degrees 2 theta at a scan rate of 1.5 degrees/minute.  The random powder mounts are analyzed over an angular range of 2-60 degrees 2 theta at a rate of one degree/minute using a sample spinner to reduce the effects of preferred orientation.

Quantitative analyses of the diffraction data are done using integrated peak areas (derived from peak deconvolution / profile-fitting techniques) and empirical and calculated reference intensity ratio (RIR) factors determined specifically for the diffractometer used for data collection.  The weight fractions of the clay minerals (and clay-size rock-forming minerals) are determined for the clay mounts of each sample and normalized to the weight percent clay-size material determined by the weighing procedure described above.  The weight fractions of the minerals present in the random powder mounts (including >4 micron clay minerals) are calculated and normalized to the weight percent sand/silt material. The whole-rock compositions are then determined by mathematically combining the XRD data from both size fractions. Determinations of mixed-layer clay type, ordering and percent expandable interlayers are done by comparing experimental diffraction data from the glycol-solvated clay aggregates with simulated one dimensional diffraction profiles generated using the program NEWMOD written by R. C. Reynolds.