Specimen data for Dolomite

Tom Mortimer catalog number: 1649

Identification method: identification by EDS analysis:

Notes: Initially thought these rhombs might be ankerite, but analysis showed them to be ferroan dolomite.
The first qualitative of this and similar Westmoreland specimens indicated the ankerite species, Ca(Fe, Mg)(CO₃)₂. (This EDS detector did not respond to elements lighter than sodium and had a relatively poor Mg response.)
A 2018 quantitative EDS analysis (BC277) indicated insufficient iron (Fe) for this to be ankerite. The indicated chemistry from this analysis was Ca(Mg_0.27, Fe_0.23)O_2.7 , normalized for one atom of Ca. The carbon was not quantified. Thus, Mg dominant over Fe and therefore ferroan dolomite.
A lengthy 2018 discussion on mindat.org indicated that ankerite is quite rare and that most specimens labeled ankerite are actually ferroan dolomite.