268 COSMOS. 



the simple minerals which characterize the more generally 

 diffused Plutonic and erupted rocks, as well as those on which 

 they have exercised a metamorphic action, have been produced 

 in a crystalline state, and with perfect identity, in artificial 

 mineral products. We must, however, distinguish here be- 

 tween the scoriae accidentally formed, and those which have 

 been designedly produced by chemists. To the former belong 

 feldspar, mica, augite, olivine, hornblende, crystallized oxyd 

 of iron, magnetic iron in octahedral crystals, and metallic 

 titanium ;* to the latter, garnets, idocrase, rubies (equal in 

 hardness to those found in the East), olivine, and augite. t 

 These minerals constitute the main constituents of granite, 

 gneiss, and mica schist, of basalt, dolerite, and many porphy- 

 ries. The artificial production of feldspar and mica is of most 

 especial geognostic importance with reference to the theory of 

 the formation of gneiss by the metamorphic agency of argilla- 

 ceous schist, which contains all the constituents of granite, 



* In scoria?, ciystals of feldspar have been discovered by Heine in 

 the refuse of a furnace for copper fusing, near Sangerhausen, and ana- 

 lyzed by Kersten (Poggend., Annalen, bd. xxxiii., s. 337); crystals of 

 augite in scoriae, at Sahle (Mitscherlich, in the Abh^Jidl. der Akad. zu 

 Berlin, 1822-23, s. 40); of olivine by Seifstrom (Leonhard, Basali-Ge- 

 Hide, bd. ii., s. 495) ; of mica in old scoriae of Scbloss Garpenberg 

 (Mitscherlich, in Leonhard, op. cit., s. 506) ; of magnetic iron in the 

 scoriae of Chatillon sur Seine (Leonhard, s. 441) ; and of micaceous iron 

 in potter's clay (Mitscherlich, in Leonhard, op. cit., s. 234). 



[See Ebelmer's papers in Ann. de Chimie et de Physique, 1847 ; also 

 Report on the Crystalline Slags, by John Pei'cy, M.D., F.R.S., and 

 William Hallows Miller, M.A., 1847. Dr. Percy, in a communication 

 W\\h which he has kindly favored me, says that the minerals which he 

 has found artificially produced and proved by analysis are Humboldtil- 

 ite, gehlenite, olivine, and magnetic oxyd of iron, in octahedral crys- 

 tals. He suggests that the circumstance of the production of gehlenite 

 at a high temperature in an iron furnace may possibly be made avail- 

 able by geologists in explaining the formation of the rocks in which the 

 natural mineral occurs, as in Fassathal in the Tyrol.] — Tr. 



t Of minerals purposely produced, w^e may mention idocrase and 

 garnet (Mitscherlich, in Poggend., Annalen der Physik, bd. xxxii., s. 

 340); ruby (Gaudin, in the Comptes Rendus de VAcad6mie de Science, 

 t. iv.. Part i., p. a99); olivine and augite (Mitscherlich and Berthier, in 

 the Annales de Chimie et de Physique, t. xxiv., p. 376). Notwithstand 

 ing the greatest possible similarity in crystalline form, and perfect iden 

 tity in chemical composition, existing, according to Gustav Rose, be- 

 tween augite and hornblende, hornblende has never been found accom- 

 f)anying augite in scoriae, nor have chemists ever succeeded in artificial- 

 y producing either hornblende or feldspar (Mitscherlich in Poggend., 

 Annalen, bd. xxxiii., s. 340, and Rose, Reise nach dem Ural, bd. ii., s 

 358 und 363). See, also, Beudant, in XheMem. de V Acad, des Sciences^ 

 t. viii., p. 221, and Becquerel's ingenious experiments in his TraU^ dt 

 I Electric'tS, t. i., p. 334 ; t. iii., p. 218; and t, v., p. 148 and 185 



