4 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 124 



groundmass in which the chondrules are embedded consists of opaque 

 material and fine-grained olivine and pyroxene, probably with some 

 plagioclase. 



The density of a piece of this meteorite was determined by measuring 

 the apparent loss of weight upon suspension in carbon tetrachloride 

 (after evacuation under a bell to remove air). It was found to be 3.75. 



Chemical composition. — The method of chemical analysis of these 

 meteorites is essentially that outlined by Duke et al (1961). Cobalt 

 was determined colorimetrically in a citrate-phosphate-borate medium 

 with nitrose-R salt, as recommended by Sandell (1959). 



Table 1. — Chemical analysis and normative mineral composition of the Allegan 

 meteorite (analysis: Maynes; norm: Mason) 

 Analysis Norm 



Fe 17.23% 

 Ni 1.54 



Co 0.09 



FeS 5.57 



Si0 2 36.65 

 TiOa 0.13 



A1 2 3 2.10 



Cr 2 3 0.51 



FeO 9.30 



MnO 0.30 



MgO 23.27 

 CaO 1.71 



Na 2 0.90 



K 2 0.08 



P2O5 0.31 



H 2 0+ 0.24 



H 2 0= 0.03 



Sum 99.96% 



The chemical analysis of Allegan is given above in the conventional 

 form expressed as metal, troilite, and oxides. This form of presenting 

 meteorite analyses involves certain assumptions; for example, that all 

 S is present as FeS, that Fe in excess of free metal and FeS is present 

 as ferrous iron, that all Ni and Co are present in the metal phase. 

 These assumptions are essentially valid for the Allegan meteorite. The 

 composition shows that it is an olivine-bronzite chondrite in Prior's 

 classification (1920). The total iron content, 28.00 percent, places it 

 in the high-iron (H) group of Urey and Craig (1953). 



The normative mineral composition, calculated from the analysis 

 as recommended by Wahl (1951) and expressed as weight percentages, 

 is also given above. The observed mineral composition agrees with 

 that calculated from the analysis. The FeO/FeO-f-MgO ratio from the 

 analysis is consistent with that deduced from the composition of the 



