54 Dr. Heddle on Mesolite and Faroelite {Mesole). 



100-014 100-21 



The sole chemical difference, therefore, between mesolite and 

 faroelite is one equivalent of silica*; but the mineralogical 

 distinctions, between typical specimens, at least, are numerous 

 and well marked. Faroelite invariably occurs either in implanted 

 and isolated globules (I observed a single instance in the island 

 of Naalsoe, where these globules were prolonged into stalactites 

 of about 3 inches in length), or as a mammillated coating of 

 the rock. These spheres, generally of a bluish colour, are, 

 though radiated in their structure, solid at the circumference as 

 at the centre, and have a decided pearly lustre on one, apparently 

 a cleavage face. Mesolite, again, is generally seen in delicate, free, 

 dead white fibres, which have no pearly lustre : in the finely- 

 crystallized Iceland specimens, as also in those from TJig, the 

 lustre is vitreous. One cavity in the rock will contain mesolite ; 

 another close by, Faroelite : when both occur in the same cavity, 

 the latter is invariably nearest the rock. At Storr, as also all 

 over Faroe, Faroelite occurs in solid spheres of a blue tint, with 

 free plumes of dead white mesolite implanted on them, perfectly 

 distinct in structure and appearance ; in fact, out of twelve zeo- 

 lites which may be found at the Storr, Faroelite is, with the ex- 

 ception of chabasie, the first which has been deposited in the 

 cavities of the rock, mesolite the last, or one of the last. Again, 

 the one mineral is of common occurrence at a locality where the 

 other is rare, or altogether absent; at the next locality the 

 reverse may hold good ; and so also it is in Faroe. 



The nomenclature of these zeolites seems to me to be in a sad 

 state of confusion : — we have mesotype, mesolite, mesole (also 



* From the analyses of Hisinger and Thomson, Faroelite seems to occur 

 at Annaklef and Bombay with the formula 



3(NaO, CaO)2SiOH3(APO^ SiO')+8HO, 

 the per-centages of which are — 



6820vi2 10000 



