Hi,
Anyone know why the total is so low for this chromite.
The interesting thing about chromites (particularly when considering oxidation state) is that the Mg and Al concentrations are very sensitivity to matrix correction and MACs used, and can change values by 1-2wt.% absolute.
Is there any chromite standard that has been independently measured?
Thanks
Ben
Hello,
Forsythe & Fisk (Proceedings of the Ocean Drilling Program, Scientific Results Vol 135, pp. 585-594, 1994) in their Table 2 reported the following additional oxides (n=62, with standard deviations in parentheses):
SiO2 0.07 (0.01), TiO2 0.12 (0.02), ZnO 0.06 (0.03), NiO 0.17 (0.02), V2O5 0.10 (0.02), Na2O 0.01 (0.01), whose sum is 0.53 wt%.
My own in-house analyses of Tiebaghi chromite USNM 117075 (n=75) give the following additional oxides:
- below the limit of detection are SiO2, CaO, Nb2O5, SO3, CoO, Na2O, and K2O;
- found were TiO2 0.11 (0.01), ZnO 0.03 (0.02), NiO 0.17 (0.01), V2O3 0.08 (0.01), sum 0.38 wt%.
These results are in generally good agreement with Forsythe & Fisk (1994).
[Note that 0.08 V2O3 is essentially equivalent to 0.10 V2O5.]
In particular, I find no CaO above detection, in contrast with the 1980 report of Jarosewich et al.
However, this is in agreement with the most recent on-line posting of the Smithsonian Microprobe Standards datasheets, where CaO is omitted from the chromite entry.
The implication is an additional ~0.4 wt% of elements in addition to those listed on the current SMS datasheet.
And the consequent atomic proportion of ferric iron would be around 24% (around 3.5 wt% Fe2O3).
It would be interesting to know if others have observed these minor elements.
Best regards,
Andrew