NEPHRITE CELT 
199 
green. In this brown staining the jade resembles somewhat the 
so-called “tomb jades” of China, and differs from the usual sur¬ 
face alteration of the Amargoza (Bahia) jade, which is white, 
according to Da Silva and Hussak. The material is translucent, 
* 
structureless megascopically, extremely fine-grained, and extreme¬ 
ly tough, so that the preparation of the powder for analysis was 
a lengthy and laborious proceeding. Although the thin section 
shows that the microstructure is irregularly felted, yet fracture 
of the piece cut out indicated a tendency to split parallel to the 
length of the celt. 
The specific gravity was determined by Dr. L. H. Adams, who 
obtained the value 2.946 at 21.5°, giving a corrected true density 
of 2.9382. The hardness is slightly less than that of quartz, or 
about 6.5. 
The thin section shows that the microtexture is that of a typical 
nephrite. The rock is made up of a densely felted mass of very 
minute fibers of tremolite, with here and there distinct patches 
of slightly coarser prismoids. The fibrous and slightly patchy 
texture is best seen between crossed nicols. The amphibole 
fibers are colorless. No other mineral could be definitely made 
out, but there are some rare, excessively minute, black grains, 
probably of iron ore. No apatite was seen. The section is tra¬ 
versed by a rather coarse network of cracks, which have a gen¬ 
eral trend in one direction and thus give rise to the more easy 
fracture parallel to the length of the celt, as mentioned above. 
Doctor Merwin very kindly exarnined the material optically. 
He states that the matted fibers are too fine to show singly under 
the microscopic; but the refractive index y is 1.625 in those frag¬ 
ments which extinguish best at a maximum angle (c A y) of 
about 16°. The lowest observed index (a) is 1.597. These op¬ 
tical properties are essentially identical with those of a water-clear 
tremolite from Switzerland, described by Kreuz.'* He obtained the 
values: a1.6000, ^8= 1.6155, y = 1.6272, for the sodium 
line, and the specific gravity 2.980. We shall see that the chemi¬ 
cal composition of this tremolite is almost identical with that of 
the Paraguassa nephrite. The values for a and y are also close 
to those obtained by Ford ® on tremolites from Richville, New 
4 Ref., in Zeits. Kryst., XUX Bd., p. 213, 1911. 
5Amer. Jour. Sci., (4), Vol. XXXVII, p. 180, 1914. 
