Dr. J. 8. Hyland—Soda-Microctine, Kilmandscharo. 163 
stated, the felspar from Kilimandscharo bears a striking resemblance. 
I see nothing to lead one to conclude, that the ground-mass consists 
of felspar, which is partly monoclinic, partly triclinic, and as the 
result of my observations I must agree with M ugge,’ when he accounts 
for the phenomenon by the fineness of the striz combined with the 
small extinction-angle. 
With regard to the chemical constitution the felspar was first 
analysed by Mr. Fletcher, who was unable to remove the numerous 
inclusions of glass and other material present. By means of a 
laborious method, which occupied nearly two weeks, I was enabled 
to separate these inclusions and to satisfy myself by microscopical 
examination of the powder that it was chemically pure. 
The sp.g. was determined with aid of the Westphal balance to be 
| 2°63 at a temperature of 18° C. 
For comparison the composition of similar felspars from Svenor, 
Tyveholmen, and Pantelleria are given. 
I, Felspar from Kilimandscharo (mean of two analyses) Fletcher. 
lee do. do. do. Hyland. 
III. Felspar from the Augitesyenite of Svenor. Vogt.” 
IV. Felspar from the “« Rhombenporphyr ” of Tyveholmen. Fischer.3 
V. “ Plagioclase” from Cuddia Mida, Pantelleria. Férstner4 
Si02 | Fe203/ Al,O3| CaO | MgO | K.0 Na,O | H20 | Totals. | Oxygen ratios. Sp.g- 
ete. 
-| 60°78 | 2-32 | 23-0 2°84} trace | 4:50] 6°65] 0-21] 100°30] 9-88 pace si 
61:3 —5 | 23'1 3°02}; — 5°34) 7:11! 0:09] 99:96] 9:08 : 3:02:1 2°63 
-| 61°35} — | 22°37] 4:66! 0:04] 4:97] 6-59 — 99°98 | 8°41:2°7 :1]| 2:63 
-| 59°50] 2°47| 29°69] 5:05] 0:42] 2-50 6°38 | 1°34] 100°35} 8:°65:2:9 :1] 92-65 
66°63 | 0°72} 19:76} 0-38] 0-30] 4:86 esi — 99°96 }12°1 :3:1 :1] 2-55 
From a chemical standpoint the constitution of this felspar is 
remarkable inasmuch as there is present, in addition to a large 
amount of soda, a considerable quantity of potash. Further, that 
the 3-02 °/, of lime found cannot be accuunted for by inclusions of 
apatite or other lime-bearing minerals is evident, when we 
remember the pure condition of the powder analysed and the fact 
that the removal of the inclusions increased the amount of lime 
found, as a comparison with the analysis made by Mr. Fletcher 
shows. We may therefore consider this mineral as an admixture 
of lime, soda, and potash felspars, distinguished, however, from all 
other such compounds by the fineness of the triclinic lamellx, My 
analysis is therefore equivalent to a molecular relation of 1 Mol. Ca 
Al, Si, Og: 2:1 Mol. KA1 Si, O,: 4:02 Mol. Na Al Si; O;. There 
is therefore present 1 Mol. KAI Si, O, to 1:91 Mol. Na Al Si, O;. 
Mr. Fletcher gives An, Oro Ab,., and has therefore regarded 
the composition of anorthite as Ca, Al, Si, O,,. Forstner and others 
1 «“Feldspath aus dem Rhombenporphyr von Christiania,” Neues Jahrbuch, 
1881, 2, p. 114. 
* Brégeger, op. cit. p 261. 3 Mugge, l.c. p. 119. 
* “ Ueber die Feldspathe von Pantelleria,”’ Z. f. Kryst. vill. 2 u. 8, p. 182. 
° There was no trace of iron. 
