

KM; 



from 5 molecules = 10 MgO + 5 SiO s 

 by removing 4 MgO + 1 SiO 



and adding 4 H, 6 we have 6 MgO + 4 SiO s + 4 H 2 



or in other words, two molecules of serpentine. 



ROTH then proceeds to discuss the formation of serpentine from each of 

 the minerals which have been regarded as capable of yielding it, and shows 

 very clearly that his general conclusions are borne out by an examination 

 of established facts. One of the most interesting cases, inasmuch as it 

 involves the removal of a large amount of material, is that of the formation 

 of serpentine from a non-aluminous lime-magnesia-iron pyroxene occurring 

 at Sala, in Sweden. The following row of analyses by H. ROSE, SVANBERG 

 and LYCHNELL serve to illustrate this change. In the altered forms the water 

 has been deducted and the analysis calculated to 100. 



I. II. III. IV. V. 



Si0 2 54-80 ... 59-66 ... 63-33 ... 56-16 ... 48-77 



CaO 23-57 ... 11-55 ... 5'18 ... 0-88 ... 



MgO 16-49 ... 22-88 ... 26-31 ... 33-96 ... 48.88 



FeO 4-44 ... 5-44 ... 4-36 ... 7-74 ... 



MnO 0-82 ... 



ALO, 0-21 047 1-26 



99-57 100-00 100-00 100-00 100-00 



I. Fresh pyroxene (Salite). (H. ROSE). 



II. Altered do. with 3-12 p.c. H a O. (H. ROSE). 



III. Do. do. 4-52 (H. ROSE). 



IV. Do. do. 9-83 (SVANBERG). 



V. Serpentine with 12-33 (LYCHNELL). 



The change revealed by these analyses can be explained on the assump- 

 tion that SiO a and CaO are removed. ROTH, however, suggests the possibility 

 that some MgO may have been added. At any rate, the formation of 

 serpentine in connection with the alteration of a monoclinic pyroxene appears 

 to be established. 



The formation of serpentine by the alteration and hydration of ferro- 

 magnesian and magiiesian silicates is therefore proved beyond all question ; but 

 does this substance arise in any other way ? Its frequent association with 

 crystalline limestones and dolomites in the ophicalcites has led certain 

 observers (1) to regard it as arising from the alteration of rocks rich in 

 magnesian carbonate, and by chemical reactions in which the latter 

 substance is involved. Such a mode of origin, however, does not appear to 

 be definitely established; for the limestones and dolomites in question are 

 often extremely rich in silicates (malacolite, tremolite, &c.), from which 

 serpentine may have been derived in the ordinary way. Dr. STERRY HUNT 



(I) VOLGKR. Entwickelungs ge.chichte der Talk-glimmer Familie. 



