Scientific Intelligence — Mineralogy. 195 



Sulphur, 22-18 



Arsenic, 20-33 



Lead, 57-09 



99-60 

 This substance is analogous, in the proportions of its component 

 parts, to the Federcrz, from Wolfsberg in the Harz, analysed by 

 Henry Rose ; but the latter is a s\x\^'ho-anthnoniurct of lead, {Uln- 

 stitut. No. 590.) 



22. Scheerer on the Sunstone, and on the Microscopic Exami- 

 nation of various other Minerals. — The sunstone, or avanturinc- 

 felspar, was formerly found exclusively in the vicinity of Archangel, 

 and more particularly on the island of Cedlovatoi. It was afterwards 

 met with in Ceylon, and has been lately brought by Fiedler from the 

 neighbourhood of Lake Baikal. About a year ago Mr Weibye made 

 the interesting discovery, tliat avanturine-felspar, of great beauty, 

 occurs near the town of Tvedestrand, on the Christiania-fjord."** This 

 caused Scheei'er to undertake a more minute examination of the sub- 

 stance. It has hitherto been supposed that the peculiar glittering 

 reflection of light, which it exhibits when turned in particular direc- 

 tions, proceeds either from extremely fine fissures in its interior, or 

 from small imbedded plates of mica. A microscopical and chemical 

 investigation has proved to Scheerer that this is not the case, and 

 that the play of light in the avanturine-felspar proceeds from small 

 lamellar crystals of iron-glance, which are disseminated through its 

 mass. Our space does not permit us to give the interesting details 

 communicated by Scheerer regarding the microscopic structure of the 

 sunstone and other minerals, but we exti-act the following general 

 results of his investigations. 1. Certain felspars contain microscopic 

 crystals of iron -glance, and probably sometimes of titanic iron, which 

 are imbedded in a regular manner in their mass. The relative propor- 

 tion by weight of the interposed mineral is small, and scarcely ex- 

 ceeds from one-half to one per cent. This small quantity, however, is 

 sufficient to produce tlie beautiful play of light and of colours in the 

 sunstone. 2. Hypersthene, bronzite, diallage, and anthophyllite, from 

 various localities, contain numerous lamellfe of an interposed dark 

 coloured body, which, doubtless, give rise to the peculiar metallic 

 lustre of these minerals ; a lustre more especially visible on the most 

 distinct cleavage-faces. The relative proportion by weight of the in- 

 terposed body may amount, in many cases, to several per cent. 3, The 

 colour of the coloured felspars frequently proceeds from disseminated 

 jjulvorulent bodies, whoso relative proportion by weight seems, for the 

 most part, to be inconsiderable. — It further results, that the chemical 

 analysis of the minerals included under 2, cannot afford perfectly 



* Small portions of sunstone were also found some years ago by 

 Scheerer, in tlie island of llitteroe, as stated in the second part of the 

 Gaea Norvegica, p. 323. The felspar of the sunstone from this locality, 

 ns well a3 of that from Tveilestrand, is an oligoclase, but this is not 

 alwaj-s the case with the sunstone from other places. 



