Mr. Brooke 07i Poonahlite aw^Z other Minerals. 109 



of Professor Whewell appear to me to be just. The crystalline 

 form must be affected by the state of the combination ; and 

 arbitrary or hypothetical statements may impede our attain- 

 ment of correct views on a subject of prime importance in 

 mineralogy. 



But I cannot yet see the propriety of sacrificing the con- 

 cise and graphic perspicuity of the Berzelian symbols, for the 

 purpose of reducing them to a notation, perhaps not very 

 much more generally appHcable to mathematical use; jar less 

 so to that of temporary record and tabular comparison in 

 operative chemistry ; and in mineralogy of hazardous admissi- 

 bility. Yours, &c. 



Plymouth, June 4, 1831. J. PridEAUX. 



XI. On Poonahlite, a new Species of Mifieral; on the Identity 

 o/'Zeagonite and Phillipsite, SfC. ; and other Mineralogical 

 Notices. By H. J. Brooke, Esq. F.R.S. L.S. Sf G.S. 



To the Editors of the Philosophical Magazirie and Amials. 

 Gentlemen, 



1SEND you herewith a few mineralogical notices, which 

 will probably interest some of your readers. 

 I am yours, &c. 

 June 11, 1831. H. J. BrOOKE. 



Thtdite. 

 In a hst of minerals which I published in 1823, as an Ap- 

 pendix to an elementary work on Crystallography, I described 

 this mineral as having a cleavage parallel to the planes of a 

 rhombic prism of 92" 30', which description was given on the 

 authority of some fragments of a reddish mineral received by 

 Mr. Heuland, from Sweden, under the name of Thulite. I since 

 find that the mineral I then measured was Bisilicate of man- 

 ganese. I have lately obtained and measured the true Thulite, 

 and have found it agree in its cleavages and angular mea- 

 surements with Epidote, as it had been before found to do by 

 Mr. Levy. 



Zeagonite. 

 In the same list of minerals I described the crystalline form 

 oi Zeagonite as an octahedron, with a scjuare base; anil I did 

 this upon the authority of a crystal from Vesuvius, so named 

 in the ticket by which it was accompanied. The crystal 1 then 

 measured lias since been called Zircon, but whether analysed 

 or not I do not know. I have lately obtained specimens of 

 the Zeagonite described by Gismondi, wliich I shall probably 



make 



