76 Professor Hausmann on Metallurgical Phemmena 



Hzed in the form of idocrase. To the most remarkable pro- 

 ductions of this kind belongs the avanturine, a sort of glass co- 

 loured by means of protoxide of copper, and oxide of antimony, 

 in which extremely delicate regular six-sided tables of copper- 

 mica (a combination of three parts of the protoxide of copper, 

 and of one part of the oxide of antimony) lie imbedded ; a 

 structure that is sometimes visible on the slags produced by 

 the fusion of copper. These phenomena display something 

 perfectly analogous to the occurrence of felspar crystals in the 

 obsidian lava. This supplies us at the same time with a proof 

 for the accuracy of that opinion, which teaches us, that most 

 crystals found in the different kinds of lava are not formed in- 

 dependent of it, and merely included in its mass ; but that they 

 are produced by being separated from the lava upon its becom- 

 ing soHd. 



The stony character of the slags occurs much more fre- 

 quently than the separation of individual crystals ; a circum- 

 stance which occasions the disappearance both of transpa- 

 rency and of glassy lustre, and leaves at the most a faint shin- 

 ing lustre on the surface of the fragments, which, instead of 

 being perfectly conchoidal, occur generally with an imperfect 

 conchoidal, an uneven, or a splintery fracture, and in conse- 

 quence of the last mentioned quality, often approximate more 

 to the crystalhne radiated structure. Such slags may be com- 

 pared with many compact intimately united mountain rocks, as 

 for example, the aphanite and compact basalt, and also with the 

 basis of many kinds of porphyry, such as eurite, clinkstone, 

 pitchstone, and pearlstone porphyries. The slowly cooled 

 Leisten and Gossen slags of the blast-furnace are of a stony na- 

 ture ; and this quality is not unfrequently found in the interior 

 of a larger mass of slags with an externally glassy texture. 

 The stripping of the glass from the blast-furnace slags, which 

 is effected by a slow cooling among the rubbish between gra- 

 dually extinguishing small coke, as is practised in the Royal 

 Foundry in Silesia, is very curious. The slags so stripped, have 

 often a great resemblance to porcelain jasper, and are usually, 

 externally, of a grey, and internally, of a dark-blue colour. 



Of all the various kinds of slags there is none that appears more 

 frequently crystallized than the silicate'of the protoxide of iron 



