152 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



yses, while agreeing well with the theoretical values required by the 

 formula 6MgO. RgC^s- ISHjO. were made upon impure material. If 

 the determination of the carbon dioxide content is correct the mineral 

 can not be pyroaurite. It is probably a mixture of hydromagnesite, 

 brucite, and limonite. 



Sjogren points out the crystallographic similarity between pyro- 

 aurite and chalcophanite. The value for c for pyroaurite is given 

 as 3.6072, calculated from the angle 10T0:10Tl==76° 30' while c for 

 chalcophanite is given as 3.52G7 from 1010: 1011=^76° 12'. Chalco- 

 phanite is a mineral very likely to occur at Langban, at least the 

 manganese member, and it is possible that pyroaurite is derived from 

 it. Since chalcophanite is derived from franklinite or jacobsite we 

 have the interesting genetic relations — hydrotalcite from spinel, 

 stichtite from chromite, pyroaurite from jacobsite through chalco- 

 phanite. 



Pyrognostics. — Before the blowpipe the mineral turns golden 

 brown, becomes magnetic, but does not fuse. In a closed tube it 

 turns brown, then golden brown, gives abundant water, and becomes 

 magnetic. 



BRUGNATELLITE. 



Aktini, Real. Ace. Line, vol. 18, p. 3, 1909. 



Pelloux, Museo Civico di Storia Naturale, Geneva, vol. 46, p. 34, 1913. 



Brugnatellite was described- in 1909 as a new mineral by Artini. 

 It occurs at an old asbestos mine in the Val Malenco. Artini's anal- 

 ysis is the only one available and the material was carefully examined 

 under the microscope and found to be homogeneous and free from 

 artinite, hydromagnesite, brucite, etc., and with but a trace of serpen- 

 tine. Artini's analysis is given below : 



These ratios give the formula 6MgO. iRoOg. COo. lO^HOo. which 

 may be written MgC03. 5Mg(0H),. FeCOH),,. 4E3O. This corre- 

 sponds to pyroaurite, less one molecule of Fe(0H)3. 



However, if we consider one molecule of Fe(0H)3 replaced by its 

 equivalent of magnesia — that is, 1| Mg(0H)2 — we get a formula 

 requiring a composition given below : 



