The Rev. S. Haughton's Notes on Mineralogy. 1^ 



peared to mc so peculiar, that I analysed it carefully with the 

 following results. — N.B. Quantity operated on =27-56 grs. 



Fatty Felspathic Mineral. 



Actual weight. Per-centage. 



Silica 18-17 grs. 65-93 



Alumina 5-78 „ 20-97 



Lime (carbonate) . . . 0-15 „ Lime . 0-30 

 Magnesia (pyrophosphate) . 0-35 „ Magnesia. 0-45 

 Loss by ignition .... 3-20 „ 11"61 



Spec. grav. = 2-319. 99-26 



The atomic proportions given by the preceding analysis are — 



Si03 1465 



AFO^ 403 



RO ...... . 32 



HO 1290 



The silica here far exceeds in amount that found in any Kaolin, 

 and in fact the relation of silica to alumina is much greater than 

 is requisite to form orthoclase. In its present state, the waxy 

 felspathic mineral of this granite, if it resulted from the decom- 

 position of orthoclase, must have done so under circumstances 

 that rendered the restoration of the silica removed as silicate of 

 potash, an operation that proceeded pari passu with the decom- 

 position of the felspar. The mineral presents no appearance of 

 disintegration, its edges of separation from the pink felspar are 

 well defined ; and although its fatty lustre makes the mineralo- 

 gist suspect the presence of water, yet it has all the appearance 

 of a mineral formed in the bosom of the molten granite at the 

 time of its eruption (or deposition?). If so formed, it should 

 not be considered as a decomposed mineral at all, but as an 

 independent hydrated silicate of alumina, formed under great 

 pressure and at a high temperature, water being present. In 

 the granites of Leinster, the margarodite mica, which is present 

 in large quantities, contains 5 or 6 per cent, of water ; and yet it 

 has never been, nor could it properly be, looked upon as the 

 result of any metamorphic action on the rock. 



I believe the hydrated aluminous silicate of Nagpur to have 

 been formed in the granite originally, or at least that, if it be 

 the result of subsequent metamoridiic action, the latter must 

 have taken place at a high heat, and, as water was present, under 

 a great pressure. If the destruction of orthoclase was necessary 

 to its formation, as fast as the silicate of potash was removed by 

 the heated water (probably red-hot), the silica must have been 

 replaced, perhaps at the expense of the quartz of the granite, 

 which is very abundant ; or, which comes to the same, tlie me- 

 tamorphosing agent was highly heated water under pressure, 



C3 



