234 William E. Ford, 



The question as to how the entrance of these various isomor- 

 phous molecules into dolomite will affect its physical characters 

 is a very complex one. If CaMg(CO.). and CaFeCCO.). form 

 a true isomorphous series the physical properties should vary 

 directly with the proportion of each molecule present. The 

 problem is rendered more complicated by the occurrence of 

 isomorphous CaCO^ and MgCO.. and in a minor degree by the 

 substitution of manganese for iron. The first relationship 

 studied was that between the variation in the specific gravity and 

 variation in composition. 



Above, in Table IV, is given all the dolomite analyses with 

 which specific gravities are recorded. These analyses have been 

 recalculated into the various carbonate molecules and the sum- 

 mation then reduced to lOO per cent. The analyses are arranged 

 according- to decreasing- amounts of the normal dolomite mole- 

 cule, CaMg(CO..).. A careful survey of the table shows 

 that there must be in some cases an error present, either in the 

 analysis itself, or in the specific gravity determination. This 

 would naturally have been expected where all analyses are 

 included without any possible critical study of their character. 

 For instance, the specific gravity of analysis No. 2 is obviously 

 too low, as is seen by comparing- it with the other analyses near 

 it in the table. In the same way the specific gravities with anal- 

 yses Nos. II, 16 and 40 are seen to be too high, while those of 

 Nos. 41 and 55 are too low. These six analyses should certainly, 

 therefore, not be considered in our calculations. There are 

 others which might be included in this list but it is felt unneces- 

 sary to push this discrimination too far, since any errors intro- 

 duced by them would not be large and would most probably 

 compensate each other. 



The water clear crystalline dolomite from the Binnental, 

 Switzerland, has very closely the composition of normal dolomite, 

 CaMg(CO;.,).. Its specific gravity was determined by Rettgers 

 as 2.87.'' We have seen that there is no evidence of any change 

 in the crystal angles of dolomite accompanying the change in 

 composition. We must conclude, therefore, that the crystal 

 lattice of dolomite remains constant in regard to its angles. If 

 we assume that the spacing of the molecular layers in the net- 



* Loc. cit. 



