70 BULLETIN" 61, U. S. DEPAKTMENT OE AGKICULIURE. 
^ Soluble minerals are deposited from solution by simple evaporation. The presence 
of^one or more soluble minerals in an evaporating solution would result in the partial 
separation of a mixture of the several compounds present, and the proportion of each 
in the "solid phase" would depend upon the solubility and proportion of each origi- 
nally present. Under certain conditions, as, for instance, the preponderance of one 
compound, when the solution reached a concentration exceeding the solubility of 
this compound, it would separate out alone until the residual solution reached a con- 
stant condition, when another compound or compounds would separate out of the 
"constant solution." The evaporation of a solution containing a number of soluble 
salines might be expected to deposit, in sequence, first a single compound and then 
always a mixture of compounds, the sequential mixtures varying with the composi- 
tion of the original solution. Just what mixture would be deposited would depend 
upon the composition of the "constant solution" formed at the several stages. Tur- 
rentine 1 has very fully discussed van't Hoff 's work upon the separation of saline com- 
pounds from solution, and it is unnecessary to repeat it here. 
Experimental data for the interpretation of results which might be expected from 
the evaporation of saline solutions occurring in the western half of the Great Basin 
are not complete. Chatard published the results of his work upon the saline solutions 
of Owens and Mono Lakes, and these have been presented in another place. They 
indicate, for a system composed of chlorides, sulphates, carbonates, and borates, the 
initial separation of calcium carbonate and ferric oxide, followed in order by trona 
and then mixtures of carbonates, chlorides, and sulphates. The last brine contained 
sodium carbonate, sodium chloride, potassium chloride, sodium borate, and nitrates. 
Apparent separation of potassium chloride or sodium borate in the first crops of crystals 
was due to the inclosure of the brine by the separated salts. The nonseparation of 
potassium and boron compounds was due to the small proportion of these compounds 
originally present. The carrying of Chatard 's experiments several steps further 
would have undoubtedly resulted in additional crops of crystals, which would have 
contained potassium and boron compounds. 
Instances of the deposition of soluble minerals by evaporation of solutions are, of 
course, common. Halite, trona, mirabilite, natron, and hanksite are deposited from 
lake waters. Of the soluble minerals named, with the exception of mirabilite. as far 
as our present information goes, none would be affected by the climatic temperature 
range. Mirabilite alters to thenardite at ordinary temperatures and when in solution 
thenardite is deposited at a temperature of 34° C, or above. This temperature is not 
uncommon in the Great Basin. 
Of the partly soluble and almost insoluble minerals our information concerning 
temperature conditions of formation is scanty. Most of them are formed by direct 
precipitation under normal temperature conditions. Pandermite, colemanite, 
tychite, and northupite would appear to require higher temperatures than would be 
afforded by the climatic temperature range. The absence of colemanite in most 
marsh deposits (reported only in Searles Marsh), and its presence in veins and as 
amygdaloids in basalt, would favor the supposition that this mineral only formed in 
the presence of heated solutions. Tychite and northupite are comparatively rare, and 
we might well conclude that some local conditions — such as the presence of a hot 
spring — favored their formation. The occurrence of howlite in association with cole- 
manite would lead to the supposition that this mineral forms under similar tempera- 
ture conditions. 2 
Secondary changes in deposited salines have not been made the subject of special 
study. Examples of the reduction of sulphates by organic matter and the formation 
of hydrogen sulphide and sulphur; the reduction of nitrates and the formation of 
ammonia have been reported. Reactions of this kind are characteristic of the more 
deeply buried beds. The formation of ulexite in nodules in the marshes would indi- 
cate this mineral to be of secondary nature. Anhydrite slowly changes over into 
gypsum. Mirabilite alters to thenardite. Glauberite alters to calcite (Dana). Ulex- 
ite alters to gypsum (Dana). 
Minerals typically occurring in veins and veinlets are kalinite, alunite, niter, 
nitrocalcite , nitromagnesite , colemanite, and howlite. All others occur in playa 
beds, in crusts and efflorescences. Glauberite has been found associated with thenar- 
dite and mirabilite. Sulphohalite has been found implanted on crystals of hanksite 
(Dana). Hanksite is found with halite, thenardite, glauberite, trona, and borax. It 
has also been found inclosed in borax crystals (Dana). 
1 Bui. No. 94, Bureau of Soils. The Occurrence of Potassium Salts in the Salines of the United States. 
2 Bui. Dept. of Geology, University of California, vol. 6. No. 9, p. 187. 
