10 MINERALOGY. 



15. Crystallization and Vital Growth Contrasted. 



While crystallization adds to the outside alone, in living- 

 growth there is addition made to every part of the sub- 

 stance. The additions in the case of the crystal are in- 

 variably the same, and all parts of it are alike ; but a 

 living growth, whether vegetable or animal, commonly 

 differs much in its different parts. A finger and a quartz 

 crystal, for example, differ widely in this respect. Far- 

 ther: while crystallization tends to straight lines and 

 exact angles, the growth of animal and vegetable sub-, 

 stances tends to curved lines, and its angles, when it 

 makes any, are not sharply defined. The branches of 

 trees are more or less rounded, and, while they have a 

 general angular arrangement with the trunk of the tree, 

 the angles are not definite. 



16. Exceptions. While what I have said of crystalli- 

 zation is generally true, there are some exceptions. The 



faces of diamonds are commonly con- 

 vex instead of plane, and the edges 

 are therefore curved. In Fig. 3 you 

 have the usual form of spathic iron 

 (carbonate of iron) and pearl spar 

 (magnesian carbonate of lime). There 

 is sometimes seen in limestone, in 

 Fig - 3 - clay-stones, and in some other rocks, 



a disposition to gather in spherical forms, and the proc- 

 ess is at least akin to crystallization. The arrangements 

 of crystals are very often in beautiful and varied imita- 

 tion of branches, leaves, and flowers. This is very fa- 

 miliar to us in the frostings on our windows. This is 

 seen in other minerals, as in alabaster in the Mammoth 

 Cave of Kentucky, where leaves, vines, and flowers are 

 imitated, some 'of the "rosettes" being, as stated by Pro- 

 fessor Dana, a foot in diameter. In all such cases the 

 curvings are in the arrangements of the crystals, each in- 

 dividual crystal probably being in its usual form. 



17. Mineral Matter in Living Substances. This sub< 



