Vol. 8, 1922 
PETROLOGY: H. S. WASHINGTON 
321 
except for a very few small shreds of muscovite and an occasional very 
minute magnetite grain. 
The pyroxene is of very variable composition, but is composed essen- 
tially of jadeite and diopside, the proportions of which vary within wide 
limits, from jadeite : diopside = 21 : 1 in No. 6, to about equal amounts 
in the Tuxtla statuette,^ and even 1 : 2^/2 in the Copan pebble. ^ Jadeite 
can evidently take up considerable amounts of diopside in solid solution. 
The material of the Tuxtla statuette, with about equal amounts of each, 
may be regarded as an end member of the series, and for this the name 
tuxtlite (pronounced tushtlite) is proposed. It may be a double salt, 
analogous to diopside or dolomite. Its optical characters (as determined 
by Merwin) are given in the paper cited, as well as its density (determined 
by Adams) and its chemical composition. From the data given later in 
table I, it would appear that the diopside- jadeite can take up albite and 
anorthite in solid solution to a certain extent, although according to Bowen,^ 
there is no experimental evidence of the solution of plagioclase in typical 
diopside, CaMgSi206. 
Some of the chemical analyses made by me of various Middle American 
jades, with two made by other analysts, are presented in table I. The 
densities and the optical properties of the pyroxene were determined on 
the same fragment which was used for the analysis. For the optical deter- 
minations I am deeply indebted to Dr. H. K- Merwin. With each analysis 
is given the composition calculated in terms of the four molecules: jadeite, 
diopside (including in some cases very small amounts of hypersthene, or 
wollastonite and a little excess ferric oxide), albite (including minute 
amounts of orthoclase), and anorthite. After allotting alumina to potash 
and soda, the invariable small excess was allotted to lime in anorthite. 
Diopside was then calculated, the usual slight excess of magnesia and 
ferrous oxide over lime forming very small amounts of hypersthene. The 
residual silica was, in every case, more than enough to form jadeite and 
less than enough to form albite; so it was distributed between these two 
molecules by the usual equations used in calculating the norm. 
The first five specimens are shown by the microscope to be quite mono- 
mineralic, composed entirely of pyroxene, and without any feldspar, 
although No. 5 shows a very few small shreds of muscovite. The section 
of No. 6 shows a little albite, in small interstitial grains; and from this 
on to No. 12 (inclusive) the amount of visible albite steadily increases. 
The jade of the Copan pebble differs markedly from the others, in texture 
and composition of the pyroxene; it has been described elsewhere.'* No. 
13 is the analysis of a small bead given me by Dr. Salazar, which is re- 
markable as being related to nephrite. It is composed of a densely felted 
mixture of pyroxene and zoisite, the latter as determined by Merwin. 
