74 Professor Hausmann on Metallurgical Phenomena 



this also must be referred the occurrence of lead-glance, zinc- 

 blende, and arsenic acid, which like veins fill up crevices in the 

 walls of silver, lead, and copper -furnaces. That in certain cir- 

 cumstances, sihcates too may be formed in a similar way, is prov- 

 ed by the appearance of crystals of a substance resembling felspar, 

 derived from fragments in the copper-furnaces at Sangerhausen, 

 to which attention has again been recently directed ; but which 

 were described by me in the year 1810, in the 4th number of 

 the Beitrage zur Berg-und Hiittenkunde, p. 86. The same 

 bodies which are found in this way, like some others formerly 

 mentioned, penetrated as vapours into masses, which either, like 

 bricks, for instance, have a certain porosity, or like sandstones 

 and others, have been transformed by heat into a softened con- 

 dition ; and are in this state deposited in forms, which resemble 

 at one time disseminated portions, at another nests of minerals, 

 and at a third, ramified veins. This phenomenon may, in an es- 

 pecial manner, serve to explain the formation of many incoherent 

 nest-like veins, which either contain ore, or consist merely of what 

 are termed vein-stones. 



The metallurgic processes afford many opportunities for the 

 study of fused masses, and the solid bodies that are produced 

 from them ; and since the rocks of igneous origin are composed 

 in a great measure of silicates, a more accurate examination of 

 the slags, which consist very frequently of silicates, is peculiarly 

 calculated to yield some clew to their formation. Among these 

 silicates, as Mitscherlich was the first to shew, the appearance of 

 several, which, both in texture and external relations, harmonizes 

 with mineral substances that are of great importance in the 

 composition of the massive mountain rocks, has contributed 

 greatly to establish more firmly the theory that assigns to them an 

 igneous origin, and to procure for it more general support. But 

 apart from the analogy that lies in their structure, the knowledge 

 of the formation of these mountain-rocks may be promoted also 

 by the study of the state of aggregation of slags. 



When silicates pass from a fused into a solid state, either a 

 glassy or a more or less crystaUine body is generated, as the 

 cooling is rapid or slow. These two kinds of aggregation are di- 

 rectly opposed to each other. In the glass, the structure is still 

 the same as it existed in the fused body : in consequence of the 



