MINERALOGY. 



91 



Adjoining these are a few minerals of the greatest rarity and inte- 

 rest. The crystals of Linariteare unique, and the specimens of Cale- 

 donite and Lanarkite, of Leadhillite, a lead hypotetracarborrate com- 

 bined with sulphate, and of the rare mineral Connellite, are among 

 the finest known of these British species. 



The borates and the class of nitrates occupy parts of Cases 37 and 

 38 ; thence to Case 40, the Cases are occupied by the class which in- 

 cludes the phosphates and arsenates, in which the isomorphism of the 

 corresponding compounds of the arsenoid element Phosphorus, and of 

 Arsenic, is so complete that the salts of their acids cannot be well 

 classified apart from each other. With these also the Vanadates find 

 their place, as being isomorphous with them. 



Here may be seen fine crystals of Erythrine, the beautiful cobalt 

 arsenate (Case 38d) ; specimens of Haidingerite (Case 38b), and of 

 Erinite (Case 37h); crystals of Lazulite (Case 39b); very fine suites 

 of Calcouranite (Case 39a) and of Cuprouranite (phosphate of Copper 

 and Uranium) (Case 39d); the beautiful blue Cornish mineral Liro- 

 conite (Case 40a) ; and splendid specimens of Apatite, Mimetesite, 

 and Pyromorphite. 



Division V. Organic Compounds. 



In Case 41 is arranged a series of organic compounds, which as Case 

 ands. occurring in the earth with constant and definite characters, indepen- 41, 

 dent of organic structure, find their place in a mineral collection. 

 Among these, Amber, in ancient times ranking in value with the 

 gems, is here exhibited in a large series of specimens. 



PSEUDOMOEPHS. 



As an addendum to the General Collection there is shown in Cases 42 Gases 

 and 43 an extensive and instructive series of Pseudomorphs, that is to *2 & 43. 

 say of minerals presenting a form not properly belonging to themselves, 

 but to other minerals which they have succeeded in position. They 

 illustrate the decomposing influences to which many minerals have 

 been subjected, and they throw valuable light on the order of succes- 

 sion in which, and the conditions under which, particular minerals 

 have been formed and deposited : in furnishing us with sure proofs of 

 conversions which we can never hope to effect in the laboratory, they 

 afford us a knowledge of facts which can be arrived at in no other way. 



IT 



