202 
NEPHRITE CELT 
locality, as this is the only known occurrence in the region, and 
is not far from the Paraguassu River. 
Hussak considers that the nephrite owes its origin to the met¬ 
amorphism of gabbros or pyroxenites, the amphibole being sec¬ 
ondary. Pyroxenite and hornblendite occur near Maracas,® about 
30 miles west of Amargoza, intruded in the gneiss and quite 
fresh and unaltered; and pyroxenite is also met with near Sitio 
Novo on the Paraguassu. My analyses of the Maracas rocks 
show that they are extremely high in manganese, containing about 
2 and 1.5 per cent, while the Paraguassu nephrite contains only 
the usual small amount. It is not probable, therefore, that the 
Bahia nephrite is derived from such rocks as I analysed. 
The material of the Minas Geraes celt (No. 3 of the Table), 
for the analysis of which only about 0.2 gram was available, 
differs greatly in composition from the other two nephrites, and 
indeed from all other nephrites. The silica and soda are both 
remarkably high, there was a slight loss of magnesia, and Fischer 
regards the analysis as of only qualitative value. It is possible, 
however, in spite of its deficiencies, that the analysis is not far 
wrong, especially as regards the silica and soda. The explana¬ 
tion of the discrepancies may be found in what has been observed 
in a study of Middle American jades now being prosecuted.® 
Most of these prove to belong* to a series made up of albite 
and diopside-jadeite, in which the silica may be as high as 67 
per cent, the percentage of soda remaining fairly constant at 
about 11 per cent. It is possible, therefore, that we have in this 
Minas Geraes “nephrite’’ an example of a similar series composed 
of albite and enstatite-diopside. Calculation shows that the analy¬ 
sis by Scheidt corresponds roughly to the composition: albite 
35.6, diopside 47.7, enstatite 10.2, and quartz 5.9 per cent. The 
magnesia accidentally lost would account for some of the excess 
silica. The observation that nephrite (but not Jadeite) occurs 
along the east coast of South America, while jadeite (but prob-, 
ably not nephrite) occurs along the west coast of Mexico and 
Central America, may have some bearing on the matter. 
8 H. S. Washington, Amer. Jour. Sci., (4), Vol. XXXVIII, p. 79, 1914. 
9 H. S. Washington, The Jade of the Tuxtla Statuette, Proc. U. S. Nat. Mus., 
Vol. IvX, No, 14, 1922; and The Jades of Middle America, Proc. Nat, Acad. Sci., 
Vol. VIII, 1922. 
