302 



DESCRIPTIONS OF MINERALS. 



to a white translucent glass. Gives water in a closed glass 

 tube. Partially decomposed by hydrochloric acid, and if 

 sulphuric acid be added to the solution, 

 a heavy white precipitate of barium sul- 

 phate is formed. ISome varieties phos- 

 phoresce when heated. 



Biff. Its twin crystals, when distinct, 

 cannot be mistaken for any other species 

 except phillipsite. Much more fusible 

 than glassy feldspar or scapolite ; does 

 not gelatinize in acids like thomsonite. 



Obs. Occurs in amygdaloid al trap, 

 and in trachyte and phonolyte, also in 

 gneiss, and metalliferous veins. Fine 

 crystallizations are found at Strontian in Scotland, and 

 in Dumbartonshire ; Andreasberg in the Hartz ; Kongs- 

 berg in Xorway. Has been found in seams in the gneiss 

 of the upper part of Xew York Island. 



The name harmotome is from the Greek harmos, a joint, 

 and temno, to cleave. 



Pliillijjtite. Xear harmotome in its cruciform crystals and 

 other characters ; but differing in containing lime in place 

 of baryta. It differs also in gelatinizing with acids and in 

 fusing with some intumescence. It also occurs in sheaf-like 

 aggregations and in radiated crystallizations. From the 

 Giant's Causeway, Capo di Bove. Vesuvius, Sicily, Iceland. 



Epistilbite. A hydrous silicate of alumina and lime. Occurs in 

 thin rhombic prism's, of a white color, with a perfect pearly cleavage 

 like stilbite. H. =4-4o. G.=2*25. Before the blowpipe froths and 

 forms a vesicular enamel. Does not gelatinize. From Iceland and 

 Hindostan, and sparingly at Bergen Hill, N. J. 



Bracaisite. Supposed to be a zeolite ; it has potassium, magnesium 

 and iron as the protoxide bases. 



Stilbite. 



In pyramidally terminated rectangular prisms usually 

 flattened parallel to the face i-%, which is the 

 direction of cleavage and is very pearly in lustre. 

 1 a 1 = 119° 16'. and 11 4°. Also" in sheaf-like ag- 

 gregations, and thin lamellar and columnar ; also 

 in pearly radiated crystallizations. 



Color white : sometimes yellow, brown or red. 

 Subtransparent to translucent. H. = 3-5-4. G.= 

 2-1-215. 





