25 % 50% 100 % 

 C ALC IT E 



10% 5% 2% 1% 0.5% 02% 

 P Y RIT E 



Figure 7-3. Effects of mineral concentration on differential-thermal curves. 



about by the lower partial pressure of expelled carbon dioxide as well as by the 

 lesser reaction time involved. Similarly, the pyrite curves at the right indicate 

 the effects of concentration. In this instance the greater complexity of reactions 

 and the presence and movement of sulfur dioxide gas produce more complicated 

 curves. The sensitivity of DTA in detecting certain minerals is illustrated by the 

 curve for 0.2 percent pyrite. 



If the diluent is not thermally inert, i.e., ordinary mixtures of minerals as 

 in rocks, soils, oil-well cuttings, etc., the same dilution effect will appear for each 

 of the thermally active minerals present, and each will appear in proportion to 

 its concentration in the sample. Figure 7-4 illustrates DTA curves for such a 

 mineral assemblage and for selected fractions thereof. A complete oil-well ditch- 

 cutting sample is represented by curve D. Portions of the same original sample 

 were separated according to color, and DTA was determined on each. Curve A 

 represents white and clear crystals making up about 20 percent of the total. 

 The small endothermic peak shows quartz; the higher temperature peak shows 

 halite (NaCl). Curve B resulted from DTA of a dark grey fraction comprising 

 about 40 percent of the total. It shows clay and shale, organic matter, and con- 

 siderable pyrite. The remaining 40 percent, a light grey fraction, yielded curve 



125 



