Twin-Crystals ofFhillipsite. 141 



Figure 4, Plate IT. represents a very remarkable one 

 among the crystals which I have observed. The portions a, 

 h, c, d, belong to one individual, while e and jT are portions of 

 the corresponding faces of the other. The substance of the 

 two individuals is so irregularly continued beyond the face of 

 composition, that it is difficult to say how this face is situated. 



The hardness of the crystals I found = 4.5, (between fluor 

 and apatite,) and their specific gravity = 2.2. 



Observations. 

 With the paper from which the preceding account is an 

 abstract I was favoured by the Baron Von Beust, a distin- 

 guished pupil of Professor Mohs, for the purpose of inserting 

 it in some future portion of my paper on the regular com- 

 position of crystallized bodies. The mineral was named by 

 him Paratomous Kouphone-spar, or cross-stone, but as, from 

 the specific gravity given =2.2, it rather appears to belong 

 to what has since been described under the name of Phillip- 

 site, I thought that the value of his communication would 

 be better appreciated if given by itself. From the circum- 

 stance of this low degree of specific gravity, I was led again 

 to ascertain that of several substances usually considered as 

 varieties of harmotome, some of which proved to agree with 

 the mineral of Baron Von Beust, while others were con- 

 siderably above it. The following were the results which I 

 obtained : — 



1. Fragments of large crystals from Strontian in Argyll- 

 shire, - - - 2.429 



2. Detached crystals from Andreasberg in the Hartz, 2.435 



3. Crystals of a greyish-white colour, occurring asso- 

 ciated with analcime in trap, at Campsie in Stirling- 

 shire, - - - 2.446 



4. Another variety from the same locality, but of a 



pale reddish-white colour, - - 2.467 



5. Large crystals from a cavity in basalt from the 

 Giant's Causeway, - - 2.259 



6. The Phillipsite of Levy from Aci Reale in Sicily, 2.200 



The last result may perhaps be liable to a slight correction. 



