404 Dr. Thomson's Analysis of Needlestone. [Deb . 



moderate heat ; and this happens equally whether the mineral 

 has been previously exposed to a red heat or not. It dissolves 

 readily, and almost completely, in oxaUc acid. The constituents 

 of this mineral are as follows : 



SiUca 48-0 



Alumina 26*5 



Soda 16-2 



Water 9-3 



100-0 



Thus natroiite contains no lime : it is obviously a compound 

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

 soda, and two atoms of water ; so that its constitution may be 

 thus denoted. 



3 Al S + S S' + 2 Aq. 



2. Skolezite is a much rarer mineral than natroiite. The only 

 specimens which Fuchs and Gehlen could procure were from 

 Ferro, Iceland, and StafFa ; but they are of opinion that it was 

 known to Haiiy, because the characters of his mesotype apply 

 very well to it ; and Werner they think classed it with his 

 needle zeolite. 



The crystals of skolelize bear a close resemblance to those of 

 natroiite, and they are of opinion that the primitive form is either 

 very nearly or absolutely the same. The only crystals in their 

 possession, or which they had seen in the possession of others, 

 were six-sided unequal angular prisms, terminated by a low four- 

 sided pyramid, the faces of which in their opinion corresponded 

 with a prism nearly similar to that of natroiite. The angles of 

 the six-sided prism were 9P 20", and 134° 20'. The angles of 

 the four-sided prism were 91° 20', and 88° 40'. The angle 

 which a face of the terminal pyramid makes with the correspond- 

 ing face of the prism is 116° 35'. Fuchs mentions that the 

 faces of the crystals upon which they operated were not so per- 

 fectly smooth as to ensure complete accuracy; though they 

 employed the reflecting goniometer. He considers it, however, 

 as demonstrated that tbe base of the prism is not strictly rectan- 

 gular, as Haliy supposed. The crystals of skolezite are all thin, 

 and never complete, one extremity only being terminated by a 

 pyramid. Two of the faces of the prism are almost always 

 broader than the remaining four, and these two are strongly 

 streaked longitudinally. It splits in the same direction as natro- 

 iite ; but the iaces thus produced are not sufficiently smooth to 

 admit of the angles being measured. 



Specific gravity, 2'214. It is hard enough to scratch glass 

 feebly. When a small portion of it is placed in the exterior 

 flame from the blow-pipe, it becomes opaque, and twists itself 

 up like a worm.* If the exterior flame be continued for some 



» Hence 1 presume the term skolezite from fxoi^^|, a worm. 



