Jarosewich et al 1980 report this analysis with a comment (#3: Total Fe reported as FeO). However, I agree with others that it is common for spinel-group mineral to have substitution of Al2O3 or Cr2O3 by Fe2O3. You can have a glimpse (estimate) of the FeO vs. Fe2O3 by using an oxygen AND cation normalization (i.e., you fix as a constraint both the total number of anion, 4 for chromite, and the total number of cation, 3). With this, you can perform a charge balance (how many positive charges, assuming only FeO, do you have to compensate for the 8 negative charges? If not enough positive charges, then you "convert" some FeO to Fe2O3 to balance the charge).
I've played with the chromite analysis given in Jarosewich. Here are the results (1st line = cation AND oxygen normalization, 2nd line = oxygen normalization only assuming all Fe as Fe2+):
Al2O3 Cr2O3 Fe2O3 FeO MgO MnO Total
Cation 9.92 60.50 3.45 9.93 15.20 0.11 99.12
Oxygen 9.92 60.50 0.00 13.04 15.20 0.11 98.77
Al Cr Fe3+ Fe2+ Mg Mn Cation O
Cation 0.376 1.540 0.084 0.267 0.730 0.003 3.000 4.000
Oxygen 0.380 1.556 0.000 0.355 0.737 0.003 3.032 4.000
Interestingly enough, with the estimate of Fe2+ / Fe3+, the total number of trivalent cation is now EXACTLY 2.000 (versus 1.937 if you assume all Fe2+ as Fe3+). This is EXACTLY the mineral formula of chromite:
(Fe2+ 0.267, Mg 0.730, Mn 0.003) (Cr 1.540, Al 0.376, Fe3+ 0.084) O4
Sum trivalent = 2.000
Sum divalent = 1.000
Now of course this is the CALCULATED (estimate!!!) of Fe2O3 - not measured. This addition of Fe3+ represent an excess of 0.346 wt-% oxygen, close to the 0.299 you report. Maybe the 0.299 actually reflect a non-published MEASUREMENT of Fe2O3 and FeO by Mössbauer or so...
QED.