On Rocks; Their Chemical and Mineral Composition, and Physical Characteristics

H. C. Salmon
1859 The Geologist  
In the definition which I have given, a mineral is described as a body possessed of a definite chemical composition and a regular physical form,—meaning by the latter particularly crystalline structure. But, while the crystalline relations of each species only vary within the narrowest limits, the chemical composition has a much wider latitude. Many individuals of the same mineral species are found, by analysis, to differ most widely in their chemical components, while the crystalline form is
more » ... ite unaltered. Now, although we are as yet unable to trace the relation between the form of a mineral and its composition, there can still be little doubt that some such relation does exist, regulated by laws yet to be discovered; consequently, when we find the same mineral species differing widely in chemical proportions, we recognise a departùre from regular although unknown laws, and seek for a cause. This we find in the doctrine of Isomorphism. This, simply stated, in the capability of two or more substances, of analogous chemical constitution, to crystallize in similar forms.
doi:10.1017/s1359465600020852 fatcat:yejab63fgbaytbfw63zadgvltu