516 



Annals New York Academy of Sciences 



Eh > —0.2 V. This conclusion was reached independently by Nagy el al. 

 (19626). The only exception is FeS, in place of which one would expect FeSa . 

 It is not too difficult to find an ad hoc assumption that accounts for this dis- 

 crepancy. For example, one can argue that the FeS was first made under 

 conditions in which it was stable, possibly even at high temperatures, and 

 that it was then brought in contact with solid sulfur at such low temperatures 

 that the rate of reaction was very slow. 



It is quite remarkable that the carbonaceous chondrites are so close to chem- 

 ical equilibrium, because intuitively one would think of an assemblage of highly 



Table 3 

 Mineralogy of Carbonaceoits Chondrites*! 



Clinopyroxene 



Olivine 



a-Iron 



7-Iron 



Magnetic troilile 



Orgueil LM 



Magnetite 



Murray F 



Haripura M 



Mokoia HT and SW 



Epsomite 



Sulfur 



Dolomite 



Breunnerite 



Pentlandite 



Higli Temperature Minerals 



5 

 6 

 6 



Trace Minerals 



* After DuFresne and Anders (1962a). 



t Estimated abundances are given as negative logarithms of 2. Thus Mighei is about 50 

 per cent olivine and 50 per cent "Murray F" mineral, with mere traces of iron, pent- 

 landite, magnetite, epsomite, and sulfur. Italicized values are of lower accuracy. 



I Trace associated with metallic iron. 



oxidized (S04=, Fe.s04 , CO,r) and reduced (S, FeS, C, organic matter) species 

 as being far from chemical equilibrium. The source for the basic pH might 

 be ammonia, and for the negative Eh, hydrogen (< 10""^ atmos.). Both would 

 conveniently disappear as the water evaporated. 



The temperature at which the aqueous stage occurred is a little harder to 

 determine. A lower limit near 0° C. is implied by the condition that the water 

 was liquid; an upper limit of 200° to 400° C. is provided by various other ob- 

 servations, e.g., the strained glass found in the Mighei carbonaceous chondrite 

 (DuFresne and Anders, 1961). As shown in figure 3, the strain disappears 

 after annealing for 48 hours at 206° C, so that after the incorporation of this 



