SALMON — ON ROCKS. 



235 



(6). Hauyne is a silicate of "ll (26), Na (15), and Ca (9), combined 

 vdth *S (12) : a variety of this last mineral, called Nosean, has a 

 sUghtly different composition, with less sulphuric acid and Ca, and 

 more =41 and Na. O.Q. of all these minerals is about 1.0. 



35. Zeolites. These minerals are hydrated silicates of Al, Oa, and 



alcalies, or seemingly hydi-ated lime-felspars. They all contain i^l 

 except 3 {Apophyllite, Damourite, and DatoUte) ; and all contain Ca 

 except 3 {Analcime, Natrolite, and Baryta-harmotome). The following 

 list includes all the principal zeolites, arranged according to their con- 

 stituents : — 



Al, Ca Scolezite, Stilbite, Heulandite^ Laumonite, Leon- 



hardite. 



Al, Ca, l^a . . Thomsonite (Comptonite), Epistilbite, Faujasite, 

 MesoHte. 



Al, Ca, K . . . Chabasite, Phillipsite (Lime-harmotome) (some 

 Na). 



Al . . . Na. . . Analcime, Natrolite (Mesotype). 



Al Ba. Baryta-harmotome.* 



^1, Ca, fia, and Strontia. Brewsterite.* 

 . . Ca, K . . . Apophyllite, Damourite. 

 . . Ca .... Datolite (with Boracic acid). 



36. Andalusite [1.33] ; ChiastoHte. Essentially an anhydrous silicate 



of Al with very often some Fe. ChiastoHte is a variety with a 

 peculiar internal structure. Bischof supposes Andalusite to originate, 

 in many instances, from felspars. In the conversion of felspars into 

 kaolin there is a diminution of Si, and an increase of Al ; and, if this 

 process were continued further, the composition of Andalusite would 

 be ultimately attained. From pseudomorphs, we find that Andalusite 

 and Chiastolite are convertible into Steatite, and the latter (Chias- 

 toHte) into Talc. 



37. Kyanite, Disthene [1.5]. Composition essentially the same as that 



of Andalusite, which mineral is found, by pseudomorphs, to be con- 

 vertible into Kyanite ; this alteration consists in the elimination of 

 the extra Si, which gives the lower O.Q. to Andalusite, and may be 

 considered as a continuation of the before-mentioned process of 

 alteration of felspars into Andalusite. 



38. Wernerite, Scapolite [.75] ; Meionite [1.0]. This mineral is essen- 



tially a silicate of Al and Ca (17), but almost always contains alcalies, 

 either Na alone, or Na with a small proportion of K : the alcalies 



* These obscure minerals are noticeable as being the only silicates of Baryta known in the 

 mineral kingdom. 



