encrusted with Carbonate of Lime and Magnesia. 18 



to the Ural Mountains. The name of Miaskite was given to this 

 rock from its occurrence in the hills in the neighbourhood of 

 Miask in Siberia. 



The second substance described under the name Miaskite was 

 also derived from the locality just named, whence it was sent to 

 Mr. Adam. JM, Dufrenoy examined it and considered it to be 

 dolomite. 



In examining the collection of minerals in the Museum of 

 Irish Industiy, I found a specimen labelled Miaskite, and 

 answering perfectly to the description given by M. Dufrenoy of 

 the substance examined by him. 



The remarkable structure of this mineral, formed, as it were, 

 of a series of ci'ystalline fibres arranged parallel to one another, 

 may be compared to a bundle of. flax or of thread completely en- 

 crusted with saline matter, the crystals of which have disposed 

 themselves in the direction of the fibres. This peculiar structure 

 gives it the aspect, at first sight, of fossil wood ; but a close ex- 

 amination led me to suspect that it was the result of pseudo- 

 morphic action. Having removed a fragment of the external 

 part of the specimen by splitting it in the direction of the fibres, 

 I introduced it into very weak hydrochloric acid ; the result ob- 

 tained, after some days of contact with the acid, confirmed my 

 supposition. The acid dissolved a quantity of lime and mag- 

 nesia, and left an asbestos-like skeleton. 



Having submitted another portion to analysis, the following 

 numbers were obtained as the result : — 



Carbonate of lime 57-483 



Carbonate of magnesia .... 40' 5 10 



Sesquioxide of iron and alumina . 0'375 



Water and organized matter . . 0"239 



Asbestiform skeleton .... 1"595 



100-202 

 If we deduct the iron, water and skeleton, &c., and calculate 

 the relative proportions of carbonate of lime and of carbonate of 

 magnesia in 100 parts of the mixed carbonates, we obtain the 

 following results : — 



Carbonate of lime 58*660 



Carbonate of magnesia .... 41-339 



99-999 

 True dolomite, or CaO CO^ + MgO CO^, would give the fol- 

 lowing composition in 100 parts : — 



Carbonate of lime 54-201 



Carbonate of magnesia .... 45-798 



99-999 



