MINERALOGICAL GEOLOGY 
399 
MINERALOGICAL GEOLOGY 
Geological Setting of Colemanite Formation. The determina¬ 
tion of the origin of the boraciferous minerals of commerce is 
strictly a geological problem. To be of genuinely practical value 
in prospecting for new deposits any theory of origin must readily 
and satisfactorily explain: (1) peculiar occurrence of the thick 
beds of nodular borate crystal, (2) restriction of the ‘‘ball borate” 
to particular horizons or zones, (3) wide dissemination of finely 
divided mineral through extensive formations, and (4) idiosyn- 
cracies of the characteristic geologic habit of the mineral. No 
hypothesis yet advanced does any of these things. Main reason 
is believed to rest in failure to recognize or appreciate fully the 
underlying principles of desert geology. It is not at all probable 
that the lime-borate, colemanite, which is now the principal borate 
of commerce, is always formed in the same way, but that different 
kinds of deposits and even similar deposits have very different 
genetic history. 
The controlling geological factors are fully a dozen in number. 
In order of their probable importance they are: (a) nature and 
age of associated sediments; (b) stratigraphic occurrence; (c) 
sedimental dependence of borate deposits; (d) anomalous en¬ 
vironment imposed by aridity; (f) physiographic setting under 
desert conditions; (g) direct influence of volcanic activities; (h) 
possible origin remote from maritime conditions; (i) necessary 
consequences of chemical affinities; (j) paragenesis of boron min¬ 
erals; (k) transmutation of intraformational minerals; (1) mul¬ 
tiple facies of boron minerals; and (m) severe restriction of lo- 
Keyes. 
Sedimentary Nature of Colemanite-yielding Deposits. The hy¬ 
pothesis of the metasomatic replacement of limestones by borates, 
