No. 2329. HYDROTALCITE GROUP OF MINERALS— FOSHAG. 



151 



Analyses and ratios of pyroaurite from Ldngban. 



Since FeO was not determined in the original analj^sis some of 

 the mineral from Langban in the United States National Museum 

 (No. 93013) was analyzed for ferrous iron, with the result, FeO, 

 0.74 per cent. The pyroaurite from Langban, however, is described 

 as opaque even under the microscope, indicating that some altera- 

 tion had taken place. The above-mentioned specimen in the United 

 States National Museum consisted of large hexagonal platy crystals, 

 which, under the microscope, showed an index of refraction of 

 approximately 1.55 and weak birefringence. The sections of the 

 crystals do not show uniform extinction, but extinguish as a mass of 

 randomly oriented plates, suggesting perhaps that they are pseudo- 

 morphic. 



The pyroaurite from Moss mine gave Sjogren on a 0.0205 g. por- 

 tion the results tabulated below : 



Analyses and ratios of pyroaurite from Mossyrufa. 



The H2O was determined by ignition loss and no doubt includes 

 some of the CO,. FeO was not determined. Both of the above 

 analyses are very unsatisfactory, but indicate that the formula of 

 pyroaurite is very probably 6MgO. RoOs- CO,. 12H20.^ 



The considerable content of MnO in Sjogren's analysis is worthy 

 of note and indicates that a manganese member of the series may 

 exist. 



Heddle described a mineral as pyroaurite from the Island of Haaf 

 Grunay. It occurred as thin seams in yellow serpentine. The anal- 



1 An analysis of pyroaurite by Mauzelius (Arkiv for Kemi. Min. ock Geol., vol. 3, 

 No. 3, 1910), has been overlooked. FcsOs, 23.20, MnO 0.21, MgO 35.08, CaO 0.54, HoO 

 33.G9, SiOo 0.29, COo 6.91. Sum 99.97. This analysis leads to the formula for pyro- 

 aurite given. 



