70 BULLETIN 61, U. S. DEPARTMENT OF AGEICULTUEE. 



V V, Soluble minei-als are deposited Irom solution by simple evaporation. The presence 

 of one or more soluble minerals in an eA-aporating 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 ()f 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 l)e 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 ^ 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 occun-ing 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 ilono 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 haA^e \indoubtedly resulted in additional crops of crystals, which would have 

 contained potassium and boron compoimds. 



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 north\xpite 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 — stich 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 Cf)nditions.^ 



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 sulpiride and sulphur; the reduction of nitrates and the formation of 

 ammonia liaA'e been reported. Pteactions of this kind are characteristic of the more 

 deeply buried l^eds. 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 tyy)icallj' occurring in veins and veinlets are kalinite, alunite, niter, 

 nitro(;alcite, nitromagnesite, colemanite, and howlite. All others occur in playa 

 beds, in crusts and oflHorescences. Glauberite has been found associated with thenar- 

 dite and mirabilite. Sulphohalite has boon found implanted on crystals of hanksite 

 (Dana). Hanksite is found Avith halite, thenardite, glauberite, trona, and borax. It 

 has also be(;n found inclosed in borax crystals (Dana). 



' Bill. No. 94, Bureau of Soils. The Oocurrenoe of Potassium Salts in the Salines of the United States. 

 2 Bill. Dept. of Geology, Qniversity of California, vol. (i, N'o. 0, p. 187. 



