NORMAL ANKERITE FEOM PHELPS COUNTY, MISSOUEL 



BY AUSTIN F. ROGERS. 



ANKERITE is a subspecies in the calcite group of carbonates to 

 which Boricky has assigned the formula: CaFeC-iOe + ^i (Ca 

 MgC'iOe), with 11 varying from one-half to ten. Normal ankerite 

 is : CaFeC206 + CaMgC-iOe, or 2CaC08 + MgCOa H- FeCOs. 



As the mineral here described was found, upon analysis, to agree 

 so closely with the theoretical for normal ankerite, a published ac- 

 count of it was thought not to be out of place. It was found by the 

 writer at an abandoned "iron bank" about six miles southwest of 

 Rolla, Phelps county, Missouri, in 1897. The mineral occurs in crys- 

 talline masses containing numerous small cavities and cracks occuijied 

 by minute crystals, which are covered with a thin coating of iron ox- 

 ide. The associated minerals include massive hematite, siderite, and 

 calcite, showing rhombohedral cleavage, and large crystals of ame- 

 thyst. 



The physical properties of the ankerite are as follows : Cleavage, 

 rhombohedral ; specific gravity, 2.99 ; luster, vitreous, inclining to 

 pearly ; color, salmon ; subtranslucent. 



An analysis was made of selected pieces containing no appreciable 

 amount of the iron oxide. Calcium, magnesium and iron were de- 

 termined by the well-known methods and calculated as oxids and car- 

 bonates. Carbon dioxid was determined by loss. The results given 

 below are the means of several determinations. 



Theory for 

 normal 

 ankerite. 



CaO 28.41 28.00 



MgO 10.20 10.03 



FeO 17.22 18.00 



CO2 44.21 43.97 



Total 100.04 100.00 



Ratio. 



CaCOs 50.74 2.00 50.00 



MgCOs 21. .34 0.99 21.00 



FeCOs 27.75 0.94 29.00 



Total 99.83 100.00 



The ratio of CaCOs : MgCOa : FeCOg is very near 2:1:1, which is 

 that for normal ankerite. This analysis agrees more closely with the 

 theoretical for normal ankerite than any published analysis I have 

 been able to find. 



MiNERALOGiCAL Laboratoey, Univ. of Kans., September 22, 1899. 

 [183]— K.U.Qr.— A viii 4— Oct, '99. 



