ORDER II. PRISMATIC HAL-BARYTE. 



ryte, as it is now determined, still contains the varie- 

 ties of several other species, which are to one another in 

 a similar relation as the different species of the genus 

 Lime-haloide, of which the fundamental form is a rhombo- 

 hedron, or those of the genus Feld-spar, whose forms are 

 hemi- or tetarto- prismatic. 



2. According to BERTHIER, the prismatic Hal-baryte 

 consists of 



Baryta 66-00. 



Sulphuric Acid 34-00. 



It is represented by the formula Ba S, which corresponds 

 to 65-63 of baryta and 34-37 of sulphuric acid. Several 

 varieties contain substances foreign to this mixture, which 

 must be considered as impurities, as silica, oxide of iron, 

 alumina, &c. If heated too quickly before the blowpipe, it 

 decrepitates ; but is difficultly fusible. Several varieties 

 emit a phosphorescent light, if carefully treated, and retain 

 this property for some time even after cooling. In the in- 

 terior flame it assumes a burning hepatic taste. Several 

 coloured varieties lose their colour on being exposed to heat. 



3. Many varieties of this species, but more particularly 

 the granular and compact ones, occur in beds accompany- 

 ing hexahedral Lead-glance, dodecahedral Garnet-blende, 

 &c. ; others are found in iron-stone beds, along with pris- 

 matic Iron ore, and brachytypous Parachrose-baryte. It is 

 frequently met with in veins, in rocks of various ages, 

 either with the above mentioned species, or with various 

 cupriferous minerals ; also with Manganese-ores, with pris- 

 matoidal Antimony-glance, and hemi-prismatic Sulphur. 

 Almost all the varieties distinguished by mineralogical au- 

 thors have been found under these circumstances. Fibrous 

 Heavy-spar occurs principally in iron-stone veins ; the im- 

 bedded globular masses are engaged in beds of clay. 



4. Compact Heavy-spar occurs in the Rammelsberg near 

 Goslar, also at Clausthal in the Hartz, at Freiberg in 

 Saxony, and at Riegelsdorf in Hessia. It is also found in 

 Staffordshire and Derbyshire, where it is termed Cawk. 

 The granular variety has been found near Frohnleithen and 



