476 John K. Wolff- — Chlorite from Northern Wyoming. 



about l/10 mm in diameter varied from 2G C to 50°, but the 

 angle of most of the cleavage flakes is about 35°. The acute 

 bisectrix, "Z," is inclined 5° to 10° to c. On account of the 

 indistinctness of the interference figures the dispersion of the 

 optic axes could not he measured satisfactorily. 



Chemical composition. — The following analysis (I) was 

 made by the writer, employing the usual methods and deter- 

 mining the water directly by the Penficld method. No 

 reaction was obtained for fluorine. To ascertain any difference 

 in the state of the water given off above 110° the mineral 

 after constant weight at that temperature was heated an hour 

 at 250° to 300° without change and at 350° for half an hour 

 with practically no change, the whole of the water going off at 

 a white heat and hence considered water of constitution. 



I . 



Mol. 



II 



SiO" = 28-81 



477 = 2 



32-1 



APO 3 ... = 26-43 

 Fe 2 3 .. = 0-24 



259 ) 

 1-5 \~ 



18-5 



MgO... = 31-21 

 FeO. .. = 0-40 



773 ) 

 5 [- 



36-7 

 0-6 



H 2 







+ 110 .. = 12-62 

 — 110 .. 0-09 

 Na'O _. = 0-35 



700 1 



5 \= 3 



12-1 



K'O ... = 0-14 



1-5 j 





CaO None 







100-29 100-0 



I. Chlorite from Wyoming. II. Leuchtenbergite, Matileon, Delesse, Ann. 

 Chim. and Phys., ix, p. 396, 1843. 



Specific gravity (pycnometer) 2 - 702. 



Pyrognostics. — Thin fragments fuse with difficulty in the 

 blowpipe to a snow-white enamel and give intense blue with 

 cobalt solution. Water givea off in closed tube is neutral or 

 very slightly alkaline. Slowly decomposed by boiling sul- 

 phuric acid and with difficulty by hydrochloric. 



Conclusion. — The simplest empirical formula from the ratios 

 of the above analysis is H Mg 3 Al 2 Si 2 O ]3 . The leuchten- 

 bergite from Mauleon, Pyrenees, of which only the old 

 analysis of Delesse (II above) is available, seems to be the 

 only chlorite containing as little iron, although the composition 

 differs greatly by the excess of alumina in the Wyoming 

 mineral, which amount is in fact exceeded by few chlorites. 

 Although it seems hardly permissible to add a new name to 

 the forty or fifty now found under the chlorite group, yet the 

 purity of this material, its peculiar chemical composition and 

 the certainty that it wilt be available in large quantity, perhaps 

 justifies the name of " Sheridanite," from the county in which 

 it occurs. 



Mineralogical Museum, Harvard University. 



