1883.] NATURAL SCIENCES OF PHILADELPHIA. 73 



it turns pink. It is decomposed by hydrochloric or sulphuric 



acid without gelatinization. 



At the request of Professor Lewis, Mr. Reuben Haines had 



made an analysis of the mineral wjth the following results : — 

 "SiO, . . . . . 43-63 



MgO B^'ll 



FeO 0-78 



Al,03 2-23 



H.O 13-20 



99-55 



Mr. Haines determined the specific gravity in a specific gravity 

 bottle containing a thermometer, the weighing being done at 60° F. 



From the composition as well as from its physical characters 

 the mineral ap|)ears to be a true serpentine. Its optical characters 

 show that it is cr^'stallized, and not a mere pseudomorph. If so, 

 the crystallization of serpentine is micaceous, as already surmised 

 by Professor Dana.^ 



As the deweylite is the result of the alteration of feldspar, so 

 the serpentine has been altered from mica (muscovite). The rela- 

 tive amount of muscovite in the adjoining graphic granite is about 

 the same as tliat of the micaceous serpentine in the deweylite. 

 Moreover in certain specimens of feldspathic deweylite, where the 

 feldspar is not corapletel}^ altered, there occur crystals of hydro- 

 muscovite (margnrodite) in place of the micaceous serpentine. 



Thus it is evident that the serpentine is changed from mica. 

 Were it not for the ready cleavage and the special optical charac- 

 ters of the serpentine, it should be regarded merely as a pseudo- 

 morph. The occasional markings at angles of 120°, though scarce 

 and imperfect, are in harmony with the same character belonging 

 to several other micaceous species among the magnesian hj^drous 

 silicates, and indicate a close relationship between the serpentine 

 group and the Yerraiculite group of minerals. 



It is intere ting to find in the quartz, deweylite and serpentine, 

 just described, such complete evidence that they have been derived 

 from the direct alteration of graphic granite ( pegmatite). While 

 the albite and muscovite havechanged intodeweylite and serpentine 

 respectively, the quartz has been broken up into cleavage frag- 

 ments, and scattered through the deweylite. This fracturing of 

 the quartz may, perhaps, give a clue to the method of alteration. 

 As^Hunt^ has suggested, in an early period of geological history, 

 when the earth's crust was hotter than now, and when a high tem- 

 perature existed even at slight depths, thermal waters would abound 

 and chemical changes would be rapid. Should such waters, highly 

 charged with magnesian salts, come in contact with the heated 



^ System of Mineralogy, p. 465. 

 '^ rhem. and Geol. Essays, p. 306. 



