Foote and Bradley — Solid Solution in Minerals. 341 



condition by careful picking. The analyses were made by 

 the usual methods. All the minerals dissolved completely in 

 hydrochloric acid. Iron and manganese were both precipitated 

 by means of bromine and ammonia. Ordinarily, manganese 

 and iron were not both present in appreciable amount and the 

 precipitate, after ignition, was considered either as Fe 2 3 or 

 Mn 3 4 . In the one case necessary, they were separated by the 

 basic acetate method. Calcium was weighed as oxide after a 

 double precipitation as oxalate. We were able to confirm the 

 observation made by Gooch and Austin* and others that 

 magnesia gives high results when precipitated from a cold 

 solution as ammonium magnesium phosphate in the usual man- 

 ner. On this account, the precipitate, after standing, was 

 filtered and redissolved in hydrochloric or nitric acid. The 

 solution was heated to boiling, and after adding a small 

 amount of ammonium phosphate, was again made alkaline 

 with ammonia. The precipitate was allowed to stand until 

 cold before filtering. Carbon dioxide was not determined 

 directly. 



Calcite. 



The specimens used for analysis were the following : 



1. Small yellowish scalenohedrons of calcite deposited on 

 well-crystallized dolomite. Locality unknown. 



2. Fine crystals of calcite, slightly etched, a combination of 

 prism with rhombohedron, deposited on a crystalline layer of 

 dolomite. This, in turn, was deposited on large scalenohedrons 

 of calcite. The dolomite of this specimen was also analyzed. 

 (See dolomite ISTo. III.) Ouray, Colorado. 



3. Small scalenohedrons of calcite deposited on well-crystal- 

 lized dolomite. Joplin, Missouri (?). 



4. Small etched scalenohedrons on a crystalline deposit of 

 dolomite. Guanajuato, Mexico. 



5. A single crystal of calcite deposited on a mass of well- 

 crystallized dolomite. Cave of the Winds, Niagara. 



6. A large, water-clear crystal of calcite, associated with pink 

 rhombohedral dolomite. Joplin, Mo. 



The analyses are given in Table I. 



Of the six analyses of calcite, all but one (No. 6) show a 

 reasonably constant amount of magnesium carbonate. The 

 average amount in the five analyses is 0'97 per cent and the 

 greatest deviation from this value amounts to only 0'17 per 

 cent. Coming as the specimens do, from a number of widely 

 separated localities, and varying greatly in habit, it is certain 

 that they were formed under varying conditions. The con- 

 clusion appears justified, therefore, that calcite is saturated by 

 * This Journal, vii, 187, 1899. 



