JUNE, 1911. ANALYSES OF STONE METEORITES — FARRINGTON. 199 
Geto fr: O; allot enough CaO to satisfy the ratio P, O; : CaO :: 1: 3.33 for 
mative. Allot F or Cl to satisfy Ca O = 0.33 Pe Os; 
d) to F not used in apatite allot Ca O to form fluorite, CaO: F:: 1:2; 
e) to Cl allot Naz O in the ratio Cl, : Naz (O) :: 1 : 1 for sodalite; 
f) to SO; allot Naz O in proportion SO; : Naz O :: 1 : 1 for noselite; 
g) to S allot Fe O in proportion S : Fe (O) :: 2:1 for pyrite; 
h) to C O: in undecomposed rocks allot Ca O in the proportion 1 : 1 for calcite. 
CO, may occur in primary calcite and cancrinite. If these minerals are secondary, 
the CO is to be neglected, since it is understood that analyses of decomposed rocks 
are not available for purposes of classification. 
Having adjusted the minor, inflexible, molecules, there remain the more impor- 
tant but variable silicate molecules, which form the great part of the mineral com- 
position, or norm, of most rocks. 
4. To Al, O; are allotted all the Ky O and Na: O not already disposed of, in the 
proportion of Al, O; : K2O + Na, O::1:1 for alkali feldspathic and feldspathoid 
(lenad) molecules. 
5. With excess of Al, O3, (Ale O3; > K,O + Naz O); 
a) to extra Al; O; allot Ca O in proportion of Al, O; : Ca O :: 1:1 for anorthite 
molecules. 
b) If there is further excess of Aly O; it is to be considered as corundum, Al, O3. 
6. With insufficient Ale O3, (Ale O; < Ke O + Naz O); 
a) Extra Naz O is alloted to Fes O3 in proportion Fe, O3 : Naz O :: 1 : 1 for acmite 
molecules. 
b) If there is still extra Naz O it is set aside for a metasilicate molecule (Naz: Si O;). 
c) When there is an excess of Ky O over Al, O; it is treated in the same manner. 
It is an extremely rare occurrence. 
7. In working with reliable analyses in which Fez O; and Fe O have been correct- 
ly determined: 
a) To Fe, Os is allotted excess of Naz O under conditions 6, a). 
b) To remaining Fe, O; is allotted available Fe O in equal proportions for mag- 
netite. 
c) If there is any excess of Fe O; it is calculated as hematite. 
Analyses in which all the iron has been determined in one form of oxidation, 
when it occurs in two, are of little value when considerable iron is present. When 
the amount of iron is very small the analyses may still be used as a means of classify- 
ing the rock. For this purpose all the iron, if given as ferric oxide, is to be calculated 
as Fe O, except that necessary to be allotted to Naz O for acmite, and then used as below. 
8. a) Extra CaO after the foregoing assignments is allotted to (Mg, Fe) O in 
proportion Ca O : (Mg, Fe) O :: 1:1 for diopside molecules. 
In all molecules where (Mg, Fe) O is present, Mg O and Fe O are to be used in 
the same proportions in which they are found after Fe O has been allotted to the 
molecules previously mentioned. That is, they are to be introduced into diopside, 
hypersthene, and olivine with the same ratio between them. 
b) If there is still an excess of Ca O it is to be set aside for calcium metasilicate 
(Ca Si Os) or subsilicate (4 Ca O . 3 Si Oz), equivalent to wollastonite or akermanite. 
Such extra Ca O will in most cases actually enter garnet, an alferric mineral. 
9. With insufficient Ca O, (CaO < (Mg, Fe) O); 
a) Extra (Mg, Fe) O is to be set aside for metasilicate or orthosilicate, hypers- 
thene or olivine, according to the amount of 51 O» present. 
