150 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



Analyses and ratios of stichtite — Continued. 



Constituents. 



SiO^.. 



AI2O3 

 CrA, 

 CaO.. 

 MgO.. 

 FeO. 

 CO2.. 

 H2O.. 



Original 

 per cent. 



2.09 



4.04 



2.24 



14.08 



Trace. 



36. 59 



.28 



6.94 



33.01 



99.27 



Recalc. 

 per cent. 



4.14 



2.28 



14.36 



37.33 



7.08 

 33.78 



0. 025 

 .022 

 .095 



.160 



1.87 



1.00 



6.00 



1.13 

 13.2 



1X1.00 



6X1-00 



1X1.13 

 12X1.10 



This leads to the formula, 6MgO. ^,0,. CO,. 12H,0. The above 

 analyses show some differences, but the results are sufficiently close 

 to 6MgO. RgOs- COg. ISHoO to be satisfactory. Below are repeated 

 the analyses as compared with the composition required by the for- 

 mula. In the case of Petterd's and the new analyses the differences 

 are not great. 



Analyses and calculated composition of stichtite. 



SiOa-. 

 Cr/Js- 

 Fe^Os- 



AI2O3- 

 FeO.. 

 MgO.. 

 CO2... 

 H,0.. 



Constituents. 



Theory (per 

 cent). 



23.39 



38.51 



6.75 



34. 57 



Hezner (per 

 cent). 



3.87 

 20.44 



1.10 

 37.12 

 10. 45 

 27.26 



Petterd (per 

 cent). 



11.5 

 9.0 



36.0 



7.2 



36.1 



Foshag (per 

 cent). 



2.09 

 14.08 



4.04 



2.24 



.28 



36.59 



6.94 

 33.01 



Pyrognostics. — Before the blowpipe stichtite glows with intense 

 light, turns light gray, and becomes magnetic, but does not fuse. 

 Heated in a closed tube the mineral turns gray and then brown, gives 

 abundant water, and becomes magnetic. 



PYROAURITE. 



IGELSTROM, Ofv. Ak. Stockli., vol. 22, p. 608, 1865. 

 Sjogren, Geol. Inst. Univ. Upsala, vol. 2, p. 59, 1894. 

 Flink, Geol. Inst. Univ. Upsala, vol. 5, p. 87, 1900. 



The mineral pyroaurite was first discovered at Langban by Igel- 

 strom who gave its composition as FeoOg. 6MgO. ISHgO. Sjogren 

 first described the crystallography of this mineral from material 

 from the Moss mine in Nordmarken. xVnalysis of material from 

 Langban gave Igelstrom the following results: 



