690 PROCEEDINGS OF THE NATIONAL MUSEUM. vou. xxxrv. 
contain less than 3 per cent. The average percentage of alumina 
for the ten is 10.22, and for the entire sixteen it becomes 6.38 per cent. 
Since the majority of these chromites have a fairly large percentage 
of alumina (an oxide that is generally reported in small amounts only 
in the analyses of meteorites), the question suggests itself. Will not 
the alumina present in the chromite account in a large part for the 
alumina reported in analyses of the feldspar—free meteorites? 
This is certainly suggested in the case of the Allegan stone, in which 
no feldspars were recognized in thin section ¢; yet its analysis ® shows 
3.04 per cent of alumina. This meteorite contains 1.3% per cent of a 
chromite having 9.67 per cent of alumina according to the analysis 
made by Stokes, and 2.63 per cent of a chromite carrying 12.38 per 
cent of alumina in the far greater amount of material worked up 
by me. 
The percentages of ne show a maximum of 20.90 and a mini- 
mum of 0.40. Twelve of the sixteen chromites contain this oxide, the 
per cents present being: 20.90, 12.22, 6.70, 5.68, 5.06, 5.00, 4.96, 4.00, 
2.76, 2.42, 0.60, and 0.40. The average for the twelve being 4.3 per 
cent. There is an apparent relation between the magnesia and the 
alumina in that nearly all of those chromites which contain magnesia 
also contain alumina. ‘There is, however, no relation between the 
amount of one oxide as compared with the amount of the other oxide. 
One chromite, for example, has 2.76 per cent of magnesia with 9.76 
per cent of alumina while another with nearly the same amount of 
magnesia, 2.42 per cent, has but 2.98 per cent of alumina. 
Ferric oxide is present:in four cases only. In two of them the 
total iron was determined as this oxide. One of the two remaining 
is so high in ferric oxide, 65.25 per cent, that it may be regarded as 
a magnetite; the other contains 10.20 per cent. Neither of the two 
last contain alumina or magnesia. 
From the data here given it appears that the majority of meteoric 
chromites contain magnesia and alumina. That there is little if any 
relation existing between the amounts of the constituent oxides. One 
only approximates a compound of the formula FeO.Cr,O;. The 
majority are of the type RO.R,O, in which RO is ferrous oxide and 
magnesium oxide and R,O, is commonly chromic oxide with alumina 
less commonly ferric oxide. 
@Proe. Wash. Acad. Sci., II, 1900, p. 46. 
bTdem., II, 1900, p. 48. 
