1820.] Dr. Thomson's Anali/sis of Needlestone. 405 



time longer, the fragment melts, and is converted into a very 

 bulky and very shining slag. When this slag is exposed to the 

 interior flame, it falls down, and forms a very vesicular and 

 slightly translucent bead. 



Skolezite in powder dissolves readily in nitric and muriatic acid 

 before it has been exposed to a red heat, and the solution, like 

 that of natrolite, assumes the form of a stiff jelly. But after 

 being heated to redness, it is no longer soluble in these acids, 

 yet it is decomposed by them, and the silica separates in the 

 state of a fine powder. OxaHc acid only dissolves a portion of 

 skolezite. The undissolved portion is not oxalate of hrae. 



Skolezite becomes electric when heated, the point of the ter- 

 minal pyramid being positive, and the other extremity negative. 



The constituents of this mineral, as determined by a number 

 of analyses, are as follows : 



SiHca 46-5 



Alumina 25*7 



Lime 14-2 



Water 13-6 



100-0 



The chief difference between skolezite and natrolite is that 

 the former contains lime in place of the soda which enters into 

 the composition of the latter. It is obviously a compound of 

 three atoms of silicate of alumina, one atom of trisilicate of 

 lime, and three atoms water; so that its constitution may be thus 

 denoted. 



3 Al S + C S' + 3 Aq. 



3. Mesolite is much more common than skolezite. IMost of 

 the specimens from Iceland and Ferro belong to it. Tyrol hke- 

 wise yields it, though not in such abundance as natrolite. By 

 Werner it is arranged under the heads of fibrous and needle 

 zeolite. Haixy confounds it under the general term mesotype. 



Its crystals resemble those of natrolite, consisting of four- 

 sided prisms terminated by a low four-sided pyramid. Fuchs 

 and Gehlen met with no specimens of six and eight-sided 

 prisms, though they suppose that such exist. The angles of the 

 lour-sided prism were found by the reflecting goniometer to be 

 91° 25', and 88= 35'. They were not able to determine the angle 

 which a face of the terminating pyramid made with a corres- 

 ponding face of the prism for want of good specimens. 



The specific gravity is stated to be 2-63 ; but I take it for 

 granted that there is an error of the press, and that the true 

 number ought to be 2*263 ; for Dr. Freyssmuth took the specific 

 gravity of a Bohemian mesolite, of which he published an ana- 

 lysis last year, and found it 2-333.* And I am not aware that 



• Schweigjjer'B Journal, xxt. 426, 



