248 Dr J. Reinhard Blum on Pseudomorphous Minerals. 



minerals, is actually of metamorphic origin. The occurrence 

 of so many pseudomorphs, consisting of steatite, an allied 

 mineral, favours this view. The exact imitation and dull 

 lustre, leave little doubt that they are actually altered crys- 

 tals. Besides, instances of olivine altei'ed to a greenish or 

 brownish-yellow steatitic mineral have been described by 

 Reuss, as occurring in Bohemia and elsewhere. 



Hornblende, with the form of Augite. — The uralite of Rose, 

 a mineral with the form of hornblende and cleavage of au- 

 gite, Dr Blum shews to be an altered hornblende. He men- 

 tions various instances of the singular mixture or union of 

 the two minerals, which he explains by supposing this change 

 to have been partially carried out. He describes druses of 

 crystals from Arendal, Norway, which have the form of horn- 

 blende, but nothing of its texture within, and which he con- 

 cludes, therefoi'e, to be pseudomorphs of hornblende. Other 

 examples of this kind of pseudomorph are said to occur in 

 porphyry near Miask, near Predazzo in the Tyrol, at Mysore 

 in Hindostan, and elsewhere. Dr Blum also mentions a 

 greenish- white augite from Orange County, New York, in the 

 Leonhard collections, which he supposes to have undergone 

 the same change from hornblende. This is indicated both 

 by its structure and angles. 



The metamorphosis in the composition producing this 

 change is, in general, an increase of the bases. The varieties 

 of the two minerals differ so much, that it becomes difficult 

 to represent the change by means of the formulas. 



Chlorite, with the form of Hornblende. — At Greiner, in the 

 Tyrol, there is a deposit of mica-slate situated between gneiss 

 and hornblende rock ; and the hornblende is changed to a leek- 

 green and dark-green chlorite, some of the folia of which are 

 an inch or more broad. Rose describes similar facts, and 

 mentions some crystals of hornblende that were chlorite ex- 

 ternally, to a line or more in depth. 



Bronm Iron Ore with the form of Pyrites. — The change of 

 pyrites to brown iron ore appears to be a very common one 

 in nature, and is in pi'ogress at the pi'esenttime. It consists 

 in the removal of the sulphur from the pyrites (sulphuret of 

 iron), and the substitution of oxygen and water, and is sup- 



