542 Chronicles of Science. [Oct., 



Externally these nodules are coated with brown iron-ore derived 

 from the decomposition of the mispickel, whilst internally they 

 are traversed by fissures, the walls of which are studded with 

 crystals of scorodite and pharmacosiderite, associated with much 

 native gold, partly in dendritic and moss-like forms, and partly 

 crystallized in cubes and octohedra. Finally, the writer calls 

 attention to the auriferous quartz of Burnt Hickory, S.W. of 

 Ackworth, where the gold is found in association with brown iron- 

 ore and native sulphur. Originally the precious metal doubtless 

 existed in the form of auriferous iron-pyrites ; and the decom- 

 position of this mineral has yielded the sulphur and oxide of iron. 

 The sulphur occurs in the cavities of the loose brown iron-ore, and 

 in some cases assumes the form of crystals, pseudomorphous after 

 those of iron-pyrites. To explain the decomposition of the mundic, 

 with the formation of these products, Herr Credner follows the 

 principle suggested long since by Gr. Kose, to account for similar 

 phenomena in the gold-deposits of Beresow in the Urals ; a decom- 

 position which may be represented by the following equation : — 



2 Fe S„ -J- 3 HO = Fe, 3 + 3 HS + S 



Professor Nordenskiold's recent examination of the rich col- 

 lection of seleniferous minerals in the Stockholm Museum, has led 

 to the detection of small quantities of the rare metal thallium in 

 certain specimens of eukairite and berzelianite, which were obtained 

 some years ago from the copper-mine of Skrikerum in Smaland. 

 Associated with these two selenides, there occurs a third mineral, 

 allied to the others in general characters, but distinguished by 

 containing thallium to the extent of not less than 19 per cent. 

 M. Nordenskiold considers this mineral to be clearly separable as 

 a distinct species, for which he proposes the name of Crookesite, as 

 an appropriate honour to the discoverer of thallium, Mr. Wilham 

 Crookes, F.K.S. 



Crookesite occurs in small opaque masses, having a vitreous 

 lustre and a lead-grey colour, a hardness of about 3, and a specific 

 gravity of 6 - 9. Before the blowpipe it colours the flame intensely 

 green, fusing to a lustrous greenish-black enamel. In hydro- 

 chloric acid the mineral is soluble. It appears to be a selenide of 

 copper, thallium, and silver; the silver, however, being referred 

 to a trace of eukairite. The formula of Crookesite may be thus 

 written:*— (Cu„ Tl, A g) Se. 



In the lignite, or brown coal, of Weissenfels, in Prussian 

 Saxony, there occurs an earthy mineral-resin described some time 

 ago by Professor Kenngott as Fyropissite. Of late years this 

 substance has become of considerable economic value from its 



* Ofversight of Kongl. Vetenskaps-Akademiens Forliandlingar, No. 10 ; and 

 ' Chemical News," July 19 ; 1867, p. 29. 



