342 Foote and Bradley — Solid Solution in Minerals. 



Table I. 



Analyses of Calcite Deposited on Dolomite. 



1 2 



Sp. gr. 2-713— 2-722 



a b Average 



MgC0 3 1-08 0-98 1-03 0-79' 0'80 O'SO 



CaC0 3 99-06 99-08 99-07 96*71 96-48 96-59 



MnCO, 0-12 0-10 O'll 2-92 2-94 2*93 



Sp. gr. undet. 

 Ouray, Colorado. 

 a b Average 



100-26 100-16 100-21 100*42 100*22 100-32 



MgC0 3 1-03 



CaC0 3 99-26 



MnCO, _ 0-17 



Sp. gr. undet. 

 Joplin, Mo. ? 



b Average 



1-06 1-04 



99-21 99-23 



0-18 0-18 



100-46 100-45 100-45 



Sp. gr. 2-741-2-769 

 Guanajuato, Mexico 



b Average 



1-07 1-12 1-09 



93-05 93-24 93*15 



5-80 5-70 5-75 



99-92 100-06 99-99 



Sp. gr. undet. 

 Cave of the Winds, Niagara 



MgC0 3 0-87 



CaC0 3 99-38 



MnCO, 0-42 



100-6' 



6 



Sp. gr. undet. 

 Joplin, Mo. 



b Average 



0-47 



0-42 



0*44 



99-65 



99-65 



99-65 



0-22 



0-22 



0-22 



100-34 100-29 10031 



approximately one per cent of magnesium carbonate at common 

 temperatures of crystallization. As we pointed out before, a 

 nearly constant value is to be expected where the amount of 

 material in solid solution is small, unless, indeed, the tempera- 

 ture variation is great. We know of no reliable data at present 

 to show whether this limit varies appreciably with extreme 

 temperature conditions. An examination of some of the 

 magnesian limestones would probably give information on this 

 point. A number of cases have been reported in which cal- 

 cites contained more magnesia than has been found by us, but 

 there is no evidence that the material analyzed was homogeneous. 

 Thus, Eisenhuth* has analyzed two calcites containing respec- 

 tively 3 - 01 and 1*52 per cent of magnesium carbonate. Both 

 of his specimens contained insoluble matter, showing the 

 material was not quite homogeneous, and it seems fully as 

 *Zeitschr. Kryst., xxxv, 582, 1901. 



