DERIVATION OF SERPENTINE. 119 



more ami more confirmed by the investigations, particularly the microscop- 

 ical ones, hitherto made, that only the alteration first described by Sand- 

 berger from olivine rocks to serpentine occurs in nature." This supposition-, 

 still maintained by some, was soon found too narrow to include the observed 

 facts, and in 1877 the same distinguished litliologist acknowledged that ser- 

 pentines or serpentinoid rocks are often formed from pyroxene and amplii- 

 bole. In view of the earlier literature of the subject it seems indeed most 

 improbable that the serpentines should have a single origin. The evi- 

 dence of actual pseudomorphism in many cases was sharply questioned 

 by Scheerer as early as 181G and later by Mr. Delesse and Dr. Hunt, and 

 no doubt some cases of erroneous determination were detected. Many in- 

 stances, however, stood the test of these challenges. All the more important 

 cases have also been reobserved since 18G7, and at present tlie number of 

 occurrences of serpentine shown by microscopic research to be derived 

 from rocks containing olivine as a subordinate constituent only or not at all 

 is on the increase. 



According to the law of thermochemistry, in any mixture of substances 

 capable of reacting upon one another the resulting compound will be that 

 whose formation is attended by the most rapid evolution of heat.* Any 

 given mineral will therefore be produced not in general under a single set 

 of conditions, but under any combination of the whole range of conditions in 

 which the formation of any other compound would be attended by a slower 

 liberation of heat. The wider the range of these conditions the commoner 

 will be the mineral, and, since conditions are never exactly repeated, the 

 assertion that a mineral is common is nearly ec^uivalent to the statement 

 that its formation is attended by the most rapid evolution of heat under 

 diverse sets of conditions. Thus, to take one of many examples, there are 

 but few ferruginous compounds which in weathering or in roasting do not 

 yield hydrous or anhydrous ferric oxide ; or, in other words, whether tlie 

 temperature be low or high, the formation of ferric oxide from almost num- 

 berless compounds of iron involves the liberation of heat more rapidly than 

 any other change. That serpentine occurs at all is sufficient evidence tliat 

 its formation is attended by the liberation of heat under certain conditions. 



' See luy iiiiper, A new law of thermocheiuistvy : Am. Jour. Sei., 3(1 series, vol. 31, 1886, p. 120, 



