DEC, 4, 1921 WASHINGTON: OBSIDIAN FROM COPAN 485 



TABLE 2 



Analyses of PantellErite Obsidian and Cognate Rocks 



(1) (2) (3) (4) 



SiOa 75.88 72.21 70.14 74.09 



AI0O3 9.67 9.72 8.61 10.88 



FeoOs 2.23 3.26 6.01 3.35 



FeO 0.83 1.07 2.73 0.42 



MgO 0.21 0.29 0.20 0.30 



CaO 0.72 0.82 0.45 0.16 



Na.0 5.13 4.42 5.44 4.56 



K2O 4.56 4.98 4.20 4.45 



H2O + ] f 1-96 0.35] 



[ 0.38 ^ \ 1.52 



HoO- J ^ 0.24 0.17 J 



TiOo 0.10 0.62 0.86 n.d. 



Zr02 n.d. n.d. 0.14 n.d. 



P2O5 n.d. 0.10 0.12 n.d. 



SO3 n.d. n.d. 0.06 n.d. 



MnO trace 0.05 0.38 n.d. 



99.71 99.74 99.86 99.73 



(1) Obsidian bead, Chichen Itza, Yucatan. Washington analyst. 



(2) Comendite, Cuddia Nera, Pantelleria. Washington analyst. H. S. Washington. 

 Jour. Geol. 21: 697. 1913. 



(3)JPantellerite, Monte San Elmo, Pantelleria. Washington analyst. H. S. Wash- 

 ington. Op. cit., p. 703. 



(4) Comendite, San Pietro, Sardinia. A. Johnsen analyst. A.Johnsen. Abh. preuss. 

 Akad. Wiss. 1912: 22. 



A chemical analysis, incomplete because of paucity of material, 

 gave the results shown in No. 1 of table 2. In the figures for silica, 

 magnesia, and the alkalies, it is much like the analysis of the Copan 

 and other common obsidians, but is somewhat lower in lime and ti- 

 tanium. In its low alumina and rather high ferric oxide (especially 

 as compared with ferrous oxide), however, it differs widely from most 

 obsidians, and shows close analogies with the more silicic pantellerites 

 and comendites, as may be seen by comparison with the other analyses 

 given in the table. 



The alumina is, indeed, so low that there is a notable excess of 

 soda and potash over the total amounts of alumina and ferric oxide, 

 so that the norm contains, not only considerable acmite, but some 

 of the sodium metasilicate molecule. 



The close analog)^ of the Chichen Itza obsidian with the peculiar 

 rocks of the Italian volcanoes will be evident, and the obsidian may 

 properly be called a hyalo-pantellerite, the glass of which is also brown. 

 The occurrence of such a lava within the area from which the votive 

 offerings may be supposed to have come is an unexpected one. Lavas 



