A question of whether Ankerite is present in Keokuk geodes has perplexed me for a number of years now. About 2002, I visited the Illinois State Geological Survey building on the University of Illinois, Urbana campus. While examining their displays, I noticed a geode which was labeled containing Ankerite. Several years later I spoke with someone who insisted that no Ankerite was present in Keokuk geodes, but instead was Ferroan Dolomite. To resolve this question, I sent three samples to Attard's Minerals for X-Ray Diffraction. The results follow.

Sample 1. Pere01 Ferroan Dolomite Geode



Graph Pere01

X-Ray Diffraction Pere01

Pos.[2Th.] Height[cts] FWHM [2Th.] d-spacing [A] Rel.Int.[%] 23.9984 15.59 01968 3.70825 2.65 30.7752 558.67 0.1574 2.90538 94.83 33.2788 11.72 0.2362 2.69231 1.99 37.2800 21.95 0.1574 2.41204 3.73 40.9440 39.70 0.2755 2.20426 6.74 44.7267 27.70 0.1968 2.02623 4.70 50.1015 38.67 0.3149 1.82073 6.56 50.7107 46.76 0.2400 1.79879 7.94

Visible Ref. Code Score Compound Name Chemical Formula * 34-0517 69 Dolomite ferroan Ca(Mg Fe)(CO∧3)∧2

This sample seems to borderline to Ankerite and would need microprobe to determine if it is one or the other. X-Ray Diffraction was performed by Attard's Minerals.