Nagy et al. : Environment of Orgueil Meteorite Parent Body 547 



The initial weight loss of the distillation residue may have been caused by the 

 loss of rehydrated water. The Ivuna thermobalance curve was very similar 

 to that of Orgueil, although the position of point Ai was less well defined. 

 Murray lost less weight than either Orgueil or Ivuna. The 3 noncarbonaceous 

 chondrites gained weight during heating, caused probably by the oxidation of 

 metal. Note that the Holbrook and Bruderheim curves were actually identi- 

 cal. The cause of the small inflection at approximately 870° C. (Ci) is not 

 known. 



One may compare the meteorite curves with published data and with those 

 in Figure 3 {right) in an attempt to evaluate the meteorite compositions. The 

 thermogravimetric patterns and the differential thermal curves of chlorites are 

 characterized by two high temperature dehydration effects; see Mielenz, 

 Schieltz and King,-''^ and Nutting.-^* Serpentine (antigorite), seems to show 

 only one principal, dehydration reaction at high temperatures.^^ Certain 

 chlorites, containing 2 polymorphic (14A and 7 A) units, had been observed to 

 exhibit 3 high temperature, dehydration effects.^^ Montmorillonite may give 

 complicated patterns; in most montmorillonites, however, the first dehydration 

 reaction occurs at temperatures lower than Ai . Some montmorillonite- 

 organic complexes show endothermic reactions in the 850 to 950° C. temperature 

 range.^" Talc^^ seems to have only 1 principal, dehydration effect, which occurs 

 close to 1000° C. Gibbsites seem to lose the majority of their water below 

 425° C. temperature.^^ 



The Orgueil curve (untreated) has 2 inflection points, Ai and Bi , similar to 

 chlorite, A2 and B2 . The thermobalance curve of a synthetic mixture con- 

 sisting of 68 weight per cent chlorite, 14 per cent magnetite, 8 per cent Mg2S04- 

 6H2O, 4 per cent elementary sulfur, and 6 per cent humic acid,* was in part 

 similar to the Orgueil curve. Other mixtures, containing either bituminous 

 petroleum, asphaltene, graphite, and/or serpentine, were less similar. The 

 thermogravimetric pattern of a chlorite sample, ground in and saturated with 

 piperidine, has shown that point Bi shifted to higher temperatures. Thermo- 

 gravimetric analysis of mineral-organic mixtures suggests that the gradual 

 decrease in weight below 600° C. temperature is caused by the volatilization of 

 complex organic matter. 



The following samples yielded curves which were dissimilar to Orgueil: 

 Recent marine sediment (from the Eastern Atlantic Ocean, 35°57'N, 07°30'W, 

 from a depth of 1350 feet, and 575 cm. below the sea bottom); top soil (from an 

 oak forest in Hartsdale, N.Y.) ; and a low temperature silicate reaction product. 

 The latter sample was prepared by mixing, in stoichiometric proportions, 

 sodium silicate and magnesium chloride solutions and allowing them to stand 

 for several days at room temperature. It has been claimed in the literature^^'^^ 

 that such a low temperature process might yield a product resembling serpen- 

 tine. X-ray diffraction patterns of the product did not show serpentine lines 

 and most of the weight loss occurred below 300° C. temperature on the thermo- 

 balance curve. The soil sample also lost most of its weight at low temperatures. 

 The Recent sediment was indicative of clay minerals other than chlorites, and 

 also probably other than montmorillonite. 



* The humic acid was prepared by I. A. Breger of the U.S. Geological Survey from Minne- 

 sota peat by low temperature alkali extraction, followed by acid precipitation and dialysis. 



