1823.] Crystalline Form of some new Minerals. 381 



Article XII. 



A Description of the Crystalline Form of some new Minerals. 

 By H. J. Brooke, Esq. FRS. FLS. &c. 



(To the Editor of the Annals of Philosophy .) 



DEAR SIR, April 19, 1822. 



Having lately been engaged in an examination of the crys- 

 talline forms of minerals, and in a few instances of their chemical 

 characters, preparatory to a list I have proposed to add to an 

 elementary introduction to crystallography, 1 have observed a 

 few new results, which form the substance of the following brief 

 notices : 



Arfwedsonite. — The benefits which mineralogy has derived 

 from the labours of Mr. Arfvvedson have induced me to associate 

 his name with this mineral, which is from Greenland, and is 

 black and foliated, and has been hitherto called ferriferous 

 hornblende. It differs, however, from hornblende in its angles, 

 its specific gravity, and its hardness. 



I am not aware of its occurrence in determinable crystalline 

 forms. It has cleavages parallel to the lateral planes, and to 

 both the diagonals of a rhombic prism of 123° 55', but there is 

 no transverse cleavage to determine whether this prism is right 

 or oblique. 



Its colour is black without a shade of green. Its cleav- 

 age planes, and its cross fracture, have a greater lustre than 

 those of amphibole, and it is scratched by amphibole. 



Specific gravity 3 - 44. 



It sometimes accompanies the sodalite from Greenland. 



Cleavelandite. — The albite, and the siliceous spar of Haussman, 

 which accompanies the green and red tourmaline, from Chester- 

 field, in Massachusetts, are varieties of the same mineral. Two 

 different names having been given to this substance, it becomes 

 necessary either to adopt one of these to the exclusion of the 

 other, or to assign a new one to the species. 



As the albite is generally blue, and sometimes red* its name 

 is consequently bad, and siliceous spar might be applied with 

 equal propriety to other substances ; I have, therefore, preferred 

 adopting the term Cleavelandite to denote the species, out of 

 respect to the Professor of Natural Philosophy in Bowdoin 

 College, United States. 



This species has cleavages in three directions, parallel to the 

 planes of a doubly oblique prism. 



" The specimen which first enabled me to determine the form i* bright blue. It 

 came from Labrador, and was given me by the Rev. C. I. Latrobe. M. Nordenskiold 

 ha* favoured me with a specimen which is red. 



