SALMON — RESEAECHES ON PSEUDOMOEPHS, 



403 



families of the mineral kingdom; it often occnrs between the 

 varieties of same species or between minerals wbicli have some 

 analogy in their chemical composition ; it is very frequent among 

 the sihcates ; it is equally so with qnartz, and in general with the 

 minerals which constitute the metalliferons deposits, or abnormal 

 rocks. 



General results. — As is seen by Table I., the enveloping and en- 

 veloped minerals are very numerons, and still, far from being- 

 exaggerated, their list might have been considerably augmented. It 

 would have sufficed, in. fact, to join to it the minerals which are 

 formed in rocks ; for the saccharoid limestone, for example, envelopes 

 a large part of the known minerals, and these latter have crystallized 

 at the same time as it. 



Besides, when a mineral has been formed, it has generally been 

 contaminated by foreign substances, amorphic or crystalline, organic 

 or inorganic, wliich have been mixed with it and have modified its 

 colour and other properties ; thus, when even a crystal is transparent, 

 it is extremely rare for it not to contain foreign substances. When 

 these substances are not visible to the naked eye, they are easily 

 recognized by the microscope, or chemical analysis. But the 

 minerals which figure in the foregoing table are only the most 

 common, and more especially those which, being crystalline, have 

 been observed in another mineral equally crystallized. 



The enveloping minerals which are the most important, and which 

 enclose the greatest number of other minerals, are particularly fluor, 

 quartz, the micas, the felspars, garnet, idocrase, scapolite, tourma- 

 line, augite, hornblende, serpentine, chlorite, talc, baryte, gypsum, 

 apatite, calcite, dolomite, chalybite. It is easy to see that they are 

 very widely spread, and that they essentially constitute rocks. On 

 the other hand, certain minerals, equally vn-de spread, such as blende, 

 hematite, olivine, sphene, only rarely enclose other minerals. 



The most common enveloped minerals are very nearly the same as 

 the enveloping minerals. We should, however, add the more widely 

 spread metallic minerals, particularly antimonite, galena, blende, 

 pyrrhotine, pyrite, towanite, magnetite, hematite, rutile, wolfram. 



The enveloping and the enveloped mineral pretty often present a 

 certain analogy in their composition. Thus, the sulphides, arsenides, 

 quartz, and the silicates, phosphates, carbonates, are found especially 

 associated with minerals of the same family. However, there is no 

 general rule in this respect, and the minerals offering the widest 

 differences in their composition may readily be found associated. 

 We thus understand how, according to the table given, quartz en- 

 velopes at least a hundred substances, and is itself enveloped by some 

 forty ; how calcite envelopes at least seventy substances, and is 

 enveloped by more than a score. Besides, the cases of quartz and 

 calcite clearly show that the enveloping or enveloped minerals may 

 belong to almost all the families. The simple bodies, the sulphides, 

 oxides, fluorides, the silicates, sulphates, phosphates, carbonates, 



