ART. 14. THE JADE OF THE TUXTLA STATUETTE WASHINGTON. 



9 



in Table 1, the crystals from the Brush collection" having been kindly 

 loaned by Dr. W. E. Ford. Those for diopside were determined by 

 Wright and Larsen^^ on the artificial mineral. 



The refractive indices of the Tuxtla diopside-jadeite approach 

 closer to those of diopside than to those of soda jadeite; this may 

 be attributed to the presence of a small amount of babingtonite 

 molecules, which would tend to raise the values for these constants. 

 It is difficult to account for the anomalous extinction angle. 



Provenance. — The question of the provenance of the jadeite (and 

 chloromelanite) that was used by the ancient inhabitants of Mexico 

 and Central America is one of great interest, and one that is as yet 

 unanswered. It was suggested years ago by Pirsson^^ that jadeite 

 may be formed through the metamorphism of highly sodic igneous 

 rocks, such as nephelite syenite or phonolite. Bearing this possibility 

 in mind, and taking into consideration the distribution through 

 North America of igneous rocks of different general chemical com- 

 positions, I have for long had a suspicion that the original localities 

 of the Mexican and Central American jadeites are along the Pacific 

 coast, rather than in the interior or near the Gulf. The establish- 

 ment of the occurrence among Mexican and Central American 

 artifacts of two distinct kinds of jadeite — a soda jadeite and a 

 diopside jadeite — might aid in throwing some light on the interest- 

 ing problem of the provenance of the material, wliich has not yet 

 been found in situ. 



Some archaeological considerations. — Although not a student ol 

 American archaeology, I venture to add a few remarks on certain 

 stylistic and archaeological features of the Tuxtla statuette; these 

 may be of interest, though they are foreign to the subject of this 

 paper. They are offered only because they are based on some gen- 

 eral archaeological principles, applicable to Mayan as well as to 



•2In view of the difflcult accessibility of the Bisiiop Jade Book it may be of interest to state the 

 principal crystallographic results of Penfield, which do not seem to have become a part of the general 

 literature of mineralogy. He found that jadeite is nionoclinic, with a : b : c=1.103 : 1 : 0.613; angle j8 = 

 72° 44J'. The planes present were : o(lOO), 7n(110), 7!(130), and t(Ill) ; with the fundamental angles. 

 u/\m=4o° 29', TO/ .e=58° 23', and .sAs=61'' 12', also aA«=72° 25'. The extinction angle on 6 (010) was 

 34% and 2V=about 70°. 



'3 Wright and Larsen, Amer. Journ. Sci., vol. 37, \>. 33, 1909. 



"L. v. Prisson, Aiher. Joura. Sci., ser. 4, vol. 1, p. 401, 1896 ; and in Bishop's Jade Book, voi. 1, 

 p. 162, 1906. 



