ORDER TT. PRISMATOIDAL HAL-BABYTE. 



seems to be a mechanical mixture of prismatoidal Hal- 

 baryte and rhombohedral Lime-haloide. 



2. The chemical composition of the present species is, 

 according to KLAPROTH, 



Strontia 56-00. 



Sulphuric Acid 42-00. 



According to BERZELIUS, these two constituents are in the 

 proportion of 56-36 : 43-64, and expressed by the formula 

 Sr S 2 . It is the pure sulphate of strontia, only accidental- 

 ly mixed with a small quantity of sulphate of baryta, oxide 

 of iron, silica, lime or water. Before the blowpipe it de- 

 crepitates and melts, without perceptibly colouring the flame, 

 into a white friable enamel! It loses its transparency on 

 being heated, and acquires a caustic taste, different from 

 that of prismatic Hal-baryte, if exposed to heat under the 

 same circumstances. Reduced to powder it phosphoresces 

 upon red hot iron. 



3. In grey wacke this species occurs but rarely ; more fre- 

 quently it is met with in modern limestone, sandstone, and 

 trap rocks, in single kidney-shaped masses, of various sizes ; 

 also in larger massive concretions, and in vesicular cavities 

 of amygdaloidal rocks. It is often associated with prisma- 

 toidal Gypsum-haloide and prismatic Sulphur in beds in 

 gypsum rocks, and occurs by itself in thin seams in marl, 

 alternating with clay and prismatoidal Gypsum-haloide. 



4. Beautiful crystals of a prismatic shape and massive 

 columnar varieties, occur in the sulphur mines of Sicily ; 

 also under the same circumstances at Bex in Switzerland, 

 and Conil near Cadiz in Spain. Tabular crystals and la- 

 mellar compositions are found in beautiful varieties at 

 Monte Viale near Verona, and in the Bristol Channel in 

 England. Magnificent crystals have been brought from 

 Strontian island, in Lake Erie in North America. Fine 

 varieties occur in the Seiseralpe in the Tyrol. The blue 

 varieties, in greywacke, have been found at Leogang in 

 Salzburg ; pale blue ones occur at Meudon near Paris, in 

 fissures of chalk flints. It occurs besides in several parts 

 of Italy, Germany, England and Scotland, Brazil, &c. The 



VOL. II. I 



