Dr J. Reinhard Blum on Pseudomorphous Minerals. 247 



found in the opal that occurs at the same locality, and finds 

 proof of this in the forms and position of the opal. 



Steatite with the form of Andalusite. — Pseudomorphs of this 

 kind have been described by Von Leonhard, and Goldfuss and 

 Bischof. The change is a simple replacement of the alumina 

 by magnesia. 



Steatite with the form of Mica. — At Monzoni, tabular crys- 

 tals of mica changed to steatite occur along with steatitic 

 spinels. At Briinn, the same occurs in a granitic rock, the 

 whole of which is altered — the felspar to kaolin, and the 

 brown mica to a yellowish-green steatite. The Thiersheim 

 granite aflfords similar changes. 



Serpentine, with the form of Augite. — Near Schwarzenberg 

 in Saxony, a serpentine occurs with the form of Sahlite, which 

 was taken for crystallized serpentine, until afterwards shewn 

 to have the angles of the latter mineral. A black augite, 

 altered to serpentine, has been found at Fahlun. 



Serpentine, ivith the form of Hornblende. — Crystals of actino- 

 lite, altered to serpentine, have been observed near Presnitz, 

 in Bohemia, and hornblende crystals at Eastin, New Jersey. 

 The greywacke of Plauen, Weischlitz, and Geilsdorf, affords 

 other localities of these hornblende pseudomorphs. 



Serpentine, with the form of Olivine. — Quenstadthas shewn 

 that crystals of serpentine from Modum in Norway have the 

 form of olivine, and in Poggendorf's Annalcn for 1835, ex- 

 plained the chemical changes passed through in turning 

 olivine into serpentine. Some of the crystals are four inches 

 long ; they usually have rounded angles and little lustre. 



Tamnau has objected to this origin of these serpentine 

 crystals, on the ground of the extensive changes that must 

 have been required in producing the wide-spread beds of ser- 

 pentine ; and also that crystals of olivine of the size of these 

 crystals of serpentine had not been observed. Other reasons 

 are brought forward by him for doubting Quenstedt's view, 

 but they appear unsatisfactory. Breithaupt has long since 

 suggested, that serpentine may be an altered hornblende rock 

 or diorite ; beds of diorite in Saxon Voigtland, sometimes 

 have the characters of serpentine, and there is good reason 

 for believinfi:, that all serpentine, as well as its contained 



