320 
PETROLOGY: H. S. WASHINGTON 
Proc. N. a. S. 
A few beads are dead white, of dull luster, and slightly crumbly. These 
have evidently been subjected to the action of fire, and the effect of this 
is clearly seen in one or two long beads which have been heated to the point 
of softening, so that they are bent and warped to such an extent that the 
longitudinal perforation is no longer straight. 
The coarse-grained, translucent, green or green and gray varieties have 
a hardness of about 6^/4, while the mottled gray and white kinds are about 
6 V2. None of this American jade shows the extreme toughness which is so 
characteristic of most jade, especially nephrite. 
Many density determinations have been made, representing the various 
color and textural varieties, from Chichen Itza, Copan, and Mexico. 
The density varies from 3.335, about that of pure jadeite, to 2.667, about 
that of oligoclase. Some characteristic densities are given later. The 
numerous determinations by Hallock, published by Clarke and Merrill,^ 
also show the wide variation in density. 
In thin section most of the coarser specimens, whether wholly green, 
mottled green and white, or wholly white or gray, are seen to be composed 
entirely of anhedral or subhedral grains of pyroxene, no other mineral 
being present. The pyroxene grains are somewhat cracked, but there 
is little other evidence of crushing. The megascopically white and gray 
material is perfectly clear and colorless, while the green specimens, and the 
green portions of those which are mottled, are of a light, slightly yellowish 
green, with slight pleochroism. The green color is obviously not caused 
by the aegirite molecule. In the green-white mottled specimens, the 
color is distributed like a stain, covering small irregular areas, and fading 
out gradually in all directions, so that some grains near the border are 
partly green and partly colorless. In some pieces the green color is seen 
megascopically to be deeper along fine cracks, indicating the presence of 
a chromium-bearing solution. The purely pyroxenic specimens, it may 
be said, are those of the higher densities. 
In other specimens, of the lower densities, and chiefly among the mottled 
green and white, mottled white and gray, and the fine-grained light pea- 
green varieties, there is more or less feldspar, which appears as a water- 
clear albite, in irregular interstitial areas or a granular mass. This albite 
very rarely shows twinning. The relative amount of albite (or oligoclase) 
varies within wide limits, from a few shreds and patches to the greater 
part of the section. As the amount of albite increases the pyroxene 
grains become smaller, more prismatic, and more scattered, until in the 
most albitic specimens the small percentage of pyroxene forms small prisms 
scattered through a matrix of albite grains. 
Apart from the pyroxene and albite, no other minerals are present, 
