SPECIFIC GRAVITY AND SYMMETRY. 361 



phosphorus as compared with red phosphorus, and prismatic sulphur as 

 compared with octahedral sulphur, contain potential energy. When the 

 change from the first to the second takes place, energy is evolved, and 

 consequently the second form is more stable. These changes are in the 

 direction of higher symmetry, and Kelvin's argument applies equally well 

 to all the changes in which minerals pass from a lower to a higher degree of 

 symmetry. To reproduce minerals of lower symmetry would require the 

 expenditure of energy. Therefore we have an energy cause why minerals 

 with high symmetry are more stable. They contain less potential energy. 

 Their formation is under the apparent law of the universe of dissipation of 

 energy. 



SPECIFIC GRAVITY AND SYMMETRY. 



Where specific gravity and symmetry work together, as in a number 

 of the illustrations mentioned, there seem to be no exceptions to the rule 

 of increase of stability with increase of specific gravity and increase hi 

 symmetry. 



But in those instances in which the specific gravity and symmetry are 

 opposed to each other it can not be predicted which will be the dominant 

 factor. For instance, calcium carbonate crystallizes as calcite (hexagonal- 

 rhombohedral ; sp. gr. 2.7135) and aragonite (orthorhombic ; sp. gr. 2.94). 

 The former is the more stable. In this case it seems that symmetry is the 

 dominant factor. Iu the aluminum silicate which crystallizes as andalusite 

 (orthorhombic; sp. gr. 3.18), sillimanite (orthorhombic; sp. gr. 3.235), and 

 cvanite (triclinic; sp. gr. 3.615), the latter is the most stable. In this case 

 it appears that the specific gravity is the determining factor. 



It is believed that when the energy relations of these changes! become 

 known it will be found that in each of these cases the more stable molecules 

 contain less potential energy. If this be true, calcite, considering both its 

 specific gravity and its symmetry, contains less energy than aragonite, and 

 cyanite less than andalusite or sillimanite. If this conjecture be true, all 

 compounds are subject to a common law. That mineral forming from a 

 compound is most stable in which the minimum energy is contained. 



The relations of symmetry and specific gravity raise some very 

 interesting questions as to the arrangement of the molecules in minerals. 

 Pressure undoubtedly tends to produce the most compact arrangement. 



