A second centrifugation is then applied to collect any sediment which remained within this supernatant liquid. Samples of this kind tend to have outer iron coatings on individual grains which must be expunged, or the resulting diffraction pattern will produce Fe peaks which are not indicative of the grain composition. Iron removal involves a solution of sodium citrate, sodium bicarbonate and sodium dithionite which act to keep the iron residue in solution. The solution is heated in a water bath at 80 C for 15 minutes and centrifuged. The iron is subsequently removed with the supernatant liquid.
Organic removal begins with acidification and extraction of carbonates.
The hydrogen peroxide is allowed to decompose so that oxidation of all the organic material is complete. After several washings of de-ionized water, the solution is centrifuged. What remains at the bottom of the centrifuge tube can then be extracted using a thin glass pipette and deposited on a glass slide to be dried overnight. The sample is then ready to be placed in a diffractometer to be subject to the bombardment of X-radiation. Characteristic peaks for quartz and illite are also evident on the chart as labeled.