212 HAROLD L. ALLING 
THE BARIUM COMPONENT 
Celsian.—Celsian BaAl,Si,Og ‘‘is monoclinic and isomorphous 
with orthoclase.’’* No triclinic isomeric form of celsian is definitely 
known. 
CARNEGIEITE 
Our knowledge of carnegieite, Na,ALSiOs, the polymer of 
nephelite, has been derived almost entirely from the researches of 
the Geophysical Laboratory of the Carnegie Institution, although 
Thugutt? obtained crystals of it by rapidly cooling “nephelite 
hydrate.’ Carnegieite was first recognized as occurring in a 
cinder cone on the island of Linosa,? east of Tunis. It is “‘chemi- 
cally, as well as physically, a feldspar, differing somewhat from 
those belonging to the orthoclase-albite-anorthite series. It may 
represent a member of a new series, containing variable amounts 
of carnegieite.”’4 It has the same chemical composition as nephelite 
but it differs therefrom by dimorphism. It is triclinic and often 
twins polysynthetically after the albite law and less frequently 
after the pericline law. Carnegieite is reported as having a specific 
gravity of 2.571 at 25°C. The reader is referred elsewhere for 
more details, especially to Bowen.5 
No better summary of the feldspar components can be offered 
than by giving a modification of a tabulation suggested by Wash- 
ington.°® : 
Fieldspar Group “Albite” Subgroup 
(R’AISi,Os) be tie (R’AISi,Os) triclinic 
(R” ALSi,O)s Monoeliniey etc) vicrseine KAISi,Os 
Albite NaAlSi,Os 
CONTalaraiSuberoup Anorthoclase (K,Na)AISi,O3 
(R’AISi,Os) Monoclinic “Anorthite” Subgroup 
Orthoclase KAISi,O (R’AL,Si.0s) triclinic 
Barbierite NaAlSi,Og Anorthite CaA1,Si.Og 
Celsian BaAl,Si,Og Carnegieite Na-ALSi.03 
tF, W. Clarke, U.S. Geol. Surv. Bull. 588, p. 35, 1914. 
2S. J. Thugutt, Newes Jahrb., Beilage Band 9 (1894), p. 561. | 
3H. S. Washington, Jour. Geol., XVI (1908), 10; H. S. Washington and F. E. 
Wright, Amer. Jour. Sci. (4), XXVI (1908), 187, and XXIX (1910), 52-70. 
4J. P. Iddings, Rock Minerals (1911), p. 243. 
5 N. L. Bowen, Amer. Jour. Sci. (4), XX XIII (1912), 551-73. 
6H. S. Washington, ‘Suggestion for Mineral Nomenclature,” Amer. Jour. Sct. 
(4), XX XIII (February, 1912), 140. 
