Section 2.0 - Clays and Accessory Minerals 497 Figure 3. DTA curves for silica-alumina mixtures with Al O :SiO ratios (by weight) of: 2 2 3 (A) 0; (B) 0.0983; (C) 0.3452; (D) 0.6662; (E) 1.0152; (F) 2.002; (G) 2.927; (H) 10.041; (I) ∞. [12]