THE MINERALOGRAPHY OF THE FELDSPARS 235 
be substituted for the three names in the center of the table as is 
indicated at the sides. 
Monoclinic Ratios Triclinic 
Orthoclase OrrooAbo -OrgAbro | Microcline 
Soda orthoclase | Orgo Abro -OrzAb3. | Soda microcline 
: Hypoperthite Orjo Ab3o -Or,;Ab;; | Hypo- Perthite 
ee ) te perthite | (stable) 
. Eutectoperthite | Or,; Ab;; -Or,;Abe; | Eutecto- { Anorthoclase 
Anorthoclase : 
enetast An) perthite } (metastable) 
Hyperthite Or; Abs; -OrzAbg | Hyperthite 
Potash barbierite| Orz. Abs. -Or; Aby; | Potash albite 
Barbierite Or; Aby; -Oro Abyoo | Albite 
Some criticism may arise in that the above classification is 
more detailed than is warranted by the determinations possible 
with the petrographic microscope upon natural specimens. The 
writer feels, however, that with greater care and proper emphasis, 
microscopic distinctions are possible that will approach the accuracy 
now obtainable in classifying the soda-lime series. 
THE POTASH-LIME FELDSPARS—* ORANITE”’ SERIES 
One of the strange facts of mineralogy is that the potash-lime 
feldspars are considered rare in nature, and are little discussed in 
the literature. Harker’ says ‘‘the relation between orthoclase 
and anorthite are doubtless of the same general kind [orthoclase- 
albite], though the higher melting-point of the latter mineral will 
presumably throw the eutectic point somewhat nearer to ortho- 
clase.” Bayley? remarks that “mixtures’of the potash and calcium 
molecules? are extremely rare as minerals, but that they have 
been formed experimentally in the laboratory.” All available 
data lead us to conclude that the KAISi,Os-CaAL,Si,Os system is 
similar to the potash-soda series, except that we do not have to 
consider an isomeric modification of anorthite, which reduces the 
system to one of less complexity. The eutectic temperature is 
probably higher and the lines of solubilities are nearer to the sides 
of the diagram. 
Alfred Harker, Natural History of Igneous Rocks, p. 246. 
2Wm. S. Bayley, Descriptive Mineralogy, 1917, p. 408. 
3 “Components” is to be preferred for reasons already given. 
