19 13.] ROGERS— THE NOMENCLATURE OF MINERALS. 609 



rarely consistent or logical for they are not usually coordinate and 

 not uniform for the various minerals. In the earlier editions of 

 Dana's " System " varieties were greatly subordinated but in the 

 fifth and in the current sixth edition varieties are again given| 

 prominence. As Miers^° has emphasized, the non-essential proper- 

 ties of mineral have received too much attention. The recognition 

 of this fact will naturally lead to the supression of varietal names 

 as far as possible. While often convenient their use tends to con- 

 fusion. For example iron-bearing sphalerite has been called mar- 

 matite. A sphalerite from Breitenbrunn, Saxony containing eight- 

 een per cent, of iron was named cristophite. Where draw the line 

 between marmatite and cristophite? Sphalerite usually contains 

 more or less iron. If the iron content is notable or needs to be em- 

 phasized let it be called ferriferous sphalerite. No special name is 

 necessary. 



Names should serve two purposes, which are more or less dis- 

 tinct, namely convenience and accuracy. A name serves a conveni- 

 ent purpose for distinguishing a particular variety or kind of 

 mineral found at a certain locality or one with striking proper- 

 ties found at several localities. But there are so many variations in 

 the properties of minerals that the names multiply too rapidly. Ac- 

 curacy is not attained for it is very difficult to correlate the differ- 

 ent varieties and to define them accurately. 



Isomorphism plays a very prominent part in explaining the chem- 

 ical composition of minerals for many minerals are isomorphous 

 mixtures of two end members. The gaps in isomorphous series 

 are gradually being filled in. 



The only satisfactory way of simplifying mineralogical nomencla- 

 ture is, in my opinion, to name a mineral by its predominant molecule 

 of the isomorphous series to which it belongs. If the mineral is 

 described and named before the isomorphous relations are under- 

 stood the name still stands for the predominant molecule present. 

 The other names used for varieties, isomorphous mixtures, pseudo- 

 morphs, etc., should be discarded, except in a few cases to be men- 

 tioned later. Isomorphous mixtures may be indicated by qualify- 

 ing terms, e. g., ferriferous sphalerite instead of marmatite. The 



^0 " Mineralogy," p. 2. 



