AKT. 14. THE JADE OF THE TUXTLA STATUETTE WASHINGTON. 7 



as Clarke's or ours, may be assumed to be present to account for only 

 a very small percentage of RO ; because for jadeites in which the 

 percentages of CaO, MgO, or FeO are high (as in that of the Tuxtla 

 statuette), the formation of such molecules demands more silica 

 to satisfy them than is found to be present. This is because in 

 these molecules the molecular amount of SiOj is four times that of 

 RO, while in diopside they are equal. A diopsidic molecule must, 

 of course, be assumed if the molecular amount of R2O3 is loss than 

 that of RjO+RO. It may be mentioned here, in anticipation of 

 future publication, that a stud}^ of jades from a cenote at Chichen 

 Itza, in Yucatan, now being prosecuted, shows that the presence of 

 the diopside molecule is a marked characteristic of the jades of 

 Middle America (Mexico and Central America), as contrasted with 

 those of Burma, and that the jade of the Tuxtla statuette is an end 

 member of a series of albite-jadeite rocks. 



That diopside-jadeites chemically similar to that described here 

 are not uncommon is evident from a survey of the published jadeite 

 analyses, only a few of which are given in Table 1. Many jadeite 

 analyses that show high lime and magnesia, such as those by Damour, 

 are of rather early date and hence may not be altogether satisfactory, 

 but it can not be supposed that analytical errors have been committed 

 of such magnitude as to cause serious incorrectness in the large 

 amounts of lime and magnesia shown by them. Iti is also noticeable 

 that among analyses of jadeite, (especially from Middle America), 

 there is a definite serial progression from pure soda jadeite to 

 diopside-jadeite, shown by gradually increasing amounts of lime 

 and magnesia and diminution in silica and soda, as well as by con- 

 comitant changes in densitj^. A serial progression be5^ond, from 

 diopside-jadeite to diopside, is scarcely evident. 



Examination of the analyses of jadeites published in Doelter's 

 Mineralchemie '" (which include those in Bishop's Jade Book), in- 

 dicates that there is a Yerj decided difference between man}^ of the 

 jadeites of southeast Asia and those of Mexico and Central America. 

 Most of the former are composed almost wholly of the purely sodic 

 jadeite molecule, while many of the latter contain very considerable 

 amounts of lime and magnesia, indicating the presence of the diop- 

 side molecule. It would appear that comparatively few of the 

 American jadeites are almost purely sodic. To illustrate, the follow- 

 ing table shows the averages of 15 analyses of jadeite from Burma 

 (including Tibet) (1) and of 11 from Mexico and Central America 

 (2) (taken from Doelter), the figures for only SiOj, CaO, MgO, and 

 NajO being given. The analysis of the Tuxtla statuette is included in 

 the average of No. 2. 



w C. Doelter, Haaadbucli der Mineralchemie, vol. 2, pp. 652—658, 1914. 



