VIKGINIA LOCALITIES 491 



Analyses of fresh and decomposed A llnnite from Roanoke County, Virginia 



(S. D. Gooch, analyst) 



I II III IV V 



SiO, 31.71 8.48 6.77 93.23 29.56 



TiOs 86 2.16 63.52 36.48 .31 



AI2O3 9.-32 2.57 6.98 93.02 8.67 



Ce^Oa 13.90 6.44. 11.72 88.28 12.27 



Di^Os 9.07 1.21 3.34 96.66 8.77 



La^Oa 1.25 trace 0.00 100.00 1.25 



FeaOs 11.95 47.31 100.00 0.00 0.00 



FeO 8.95 trace 0.00 0.00 0.00 



MnO 18 trace 0.00 100.00 0.18 



OaO 11.02 2.45 5.62 94.38 10.40 



MgO 96 trace 0.00 100.00 0.96 



^^^^ I .16 none 0.00 100.00 0.16 



H,0 86 29.24 100.00 0.00 0,00 



100.19 99.86 72.53 



I. Analysis of fresh allanite. 

 II. Analysis of decomposed allanite. 



III. Calculated percentage of each constituent saved. 



IV. Calculated percentage of each constituent lost. 



V. Calculated percentage loss for the entire mineral. 



The figures indicate Ntliat the decomposition of the mineral has been 

 accomplished by hydration, oxidation, carbonation, and solution — the im- 

 portant chemical reactions in the belt of weathering. 



The increase or gain in water (hydration) is large. Ferrous oxide has 

 been oxidized to ferric oxide, and it is believed that most, if not all, of it 

 has been retained, although it is not improbable that some has been lost 

 through solution. 



Absence of carbonates is indicated in the analysis, but a careful test 

 made on a separate portion of the weathered product indicated the slight 

 presence of carbonates. ^Nevertheless carbonation is regarded as one of 



The formula given by Doctor Merrill for rocks is employed here for allanite. It is as 

 follows : 



^7-^^ — 0?; and 100 — a? = 2/, 



in which A = the percentage in any constituent in the residual material ; B = the per- 

 centage of the same constituent in the fresh rock, and C = the quotient obtained by 

 dividing the percentage amount of alumina or iron oxide (iron oxide in this paper) of 

 the residual material by that in the fresh rock, the final quotient being multiplied by 

 100. X then equals the percentage of the original constituent saved in the residue, and 

 y the percentage of the same constituent lost. 



