81
V. "FINGER-PRINTING" OF SOME MESOAMERICAN OBSIDIAN ARTIFACTS
Robert N. Jack and Robert F. Heizer
ABSTRACT
A total of 176 obsidian samples are here reported on. These include 151
samples of Mesoamerican obsidian collected in January-February, 1968, from
the surface of the Olmec site of La Venta, Tabasco, Mexico, 12 excavated
samples of obsidian from La Venta, 10 obsidian pieces from the Olmec site of
Tres Zapotes, Veracruz, 2 samples from the Aztec site of Tlatelolco, and one
from the Maya site of Comalcalco. The obsidian samples have been analyzed
by non-destructive x-ray fluorescence rapid scan technique for the elements
rubidium (Rb), strontium (Sr), yttrium (Y), zirconium (Zr), and niobium (Nb).
This method has been successful in characterizing 163 of the 176 samples
(92.66%) into five chemically distinct groups. Examination of the samples in
hand specimen has revealed consistent, although usually subtle, visual char-
acteristics of each of these five chemical groups, confirming that they are
mutually distinct volcanic glasses. A geologic source has been established
for only one of these obsidian types, indicating a need for further geologic
and archaeologic sampling to identify the sources and determine the time,
mechanisms, and extent of distribution of particular obsidians in Mesoamerica
in prehistoric times.
INTRODUCTION
In addition to providing precise quantitative chemical analyses, the x-ray
fluorescence technique can provide very rapid semi-quantitative determinations
of many elements in low concentrations in a variety of samples.   It has been
shown (Jack, Carmichael and Lajoie 1967) that natural (volcanic) glasses
(obsidians and pumices) from various volcanic centers in California, western
Nevada, and southern Oregon may be characterized chemically by their minor and
trace element compositions. In that study the concentrations of 19 elements
were reported; however, for the purpose of the characterization of obsidians
from a limited geographical area, it is often sufficient to make a rapid semi-
quantitative determination of only a few elements.   In order to test the
feasibility of this method as applied to Mesoamerican obsidians, 151 obsidian
fragments collected in 1968 from the surface of the La Venta site, plus another
25 pieces of obsidian collected in the course of archaeological investigations
of the La Venta and other Mesoamerican sites, were analyzed by x-ray fluores-
cence rapid scan technique. The purpose of this note is to summarize the
results of the reconnaissance study.
82
ANALYTICAL METHOD
For very rapid semi-quantitative comparative determination of the
chemical compositions of a large number of samples by x-ray fluorescence
analysis, the most satisfactory technique is often a rapid scan over the
spectral region of the elements of interest, the data being presented on
a chart recorder. One of the most convenient spectral regions for such
determinations of trace element compositions of natural glasses (obsidians)
includes the x-ray emission lines Nb KM, Zr M., Sr KM, Rb M., Th ha, and
Pb L (0.74 angstrom to 0.99 angstrom) in which the relative Zr KM, Sr KS,
and Rb Ka intensities are particularly useful for plotting obsidian compo-
sitions. The sample (up to 1?" in diameter for the currently used sample
cup) is placed in the cup in the form of a flake or artifact (obsidian),
rock chip (pumice, rhyolite, etc.), loose grains or powder, or in the form
of a specially prepared pellet usable also for precise quantitative analy-
ses. In spite of variations in the effective sample surface of randomly
broken pieces or loosely packed grains, relative intensities of the various
spectral lines over a narrow wavelength region may be very precisely deter-
mined. Quite precise "absolute" concentrations may also be obtained in
many analytical situations by using the primary beam (continuum plus charac-
teristic radiation of the target material) scattered from the sample to
standardize the effective intensities (chart recorder deflection) from
sample to sample by varying the spectrograph tube current (Ma).
The technique utilized for this study allows the recording of the
required spectral scan of one sample in approximately 7 minutes, or, in-
cluding sample changes and resetting the instrument, at least 6 samples
per hour. No sample preparation is required other than a washing in water
if the obsidian flake is coated with soil, and trimming or breaking of the
specimen to fit the sample cup if it exceeds 1?" in length.    After setting
the counting rate at the starting angle of the scan to a standard value
(2009 counts per second for these analyses) by adjusting the spectrograph
tube current, the spectrograph scans automatically.    The measurements of
the amplitude of the spectral peaks on the chart, the computation of the
corrections for spectral interferences, and the calculation of the relative
intensities of the spectral lines for each sample can be made while other
samples are being scanned.
These analyses were made in the Department of Geology and Geophysics,
University of California, Berkeley, on a Norelco (Philips) Universal Vacuum
X-ray Spectrograph using a tungsten tube, LiF {2203 analyzing crystal, scin-
tillation detector with pulse height discrimination, and an air path. The
scans were made at 2 degrees (two-theta) per minute.
83
RESULTS OF THE ANALYSES
The results of the x-ray fluorescence scans of the La Venta surface
obsidian samples are plotted in Figure 1 as relative x-ray emission line
intensities of Rb Ka, Sr KM, and Zr Ka for each of 150 samples. One
sample only (No. 1) is not plotted as it yielded no measurable spectral
output for these elements and may in fact be non-igneous (e.g. flint).
From the plotted data in Figure 1 it is clear that there are three distinct
chemical groups represented by the surface samples from La Venta, each pre-
sumably representing a separate geologic source rock. These have been
designated types A, B, and C. Also identifiable are two other types, here
designated as types D and E, based in part upon scans of the samples from
Tres Zapotes (type D) and inspection of the obsidians in hand specimen
(types D and E). Of the 151 surface samples from La Venta, 142 fall within
these 5 groups. Average values of the two scans are plotted for samples
numbered 3, 52, 75, 78, and 89 since they are particularly small or irregu-
lar in shape.
On Figure 2 are plotted the analyses of the 12 excavated samples from
La Venta and 13 samples from Tres Zapotes, Comalcalco, and Tlatelolco sites
and the analyses of three potential geologic source obsidians (Pachuca,
Hidalgo, Mexico; El Chayal, and Ixtepeque, Guatemala). It can be seen that
21 of these 25 archaeological samples fall within 4 of the same 5 chemical
groups observed in the La Venta surface samples. The other 4 specimens
group into two pairs of relative compositions intermediate to types C and E.
The El Chayal geologic source sample plots near the group composed of
samples numered VII (La Venta) and IX (Comalcalco) and La Venta surface
samples numbered 70 and 117, perhaps indicating that El Chayal is the source
of these obsidians. However, the present sampling is too small to clearly
establish this statistically. The other two labeled samples, numbered XVI
and XVII (from Tres Zapotes site), as well as La Venta surface sample number
54, group together, suggestive of another source type. The Ixtepeque geo-
logical source material likewise plots outside the five major groups recog-
nized in the La Venta surface samples. La Venta surface samples numbered
4, 5, and 89 fall roughly into the same compositional area as the Ixtepeque
sample, but again,any correlation based upon this small number of samples
is quite uncertain. As expected, the Pachuca geologic source obsidian plots
with the obsidians of type A, supporting the opinion that these distinctive
green obsidians are from the Pachuca source.
Obsidians often are quite distinctive in appearance (e.g. the Pachuca
green obsidian), no doubt contributing in many cases to their collection
and distribution in prehistoric times. With the exception of the distinct
green obsidians, cursory inspection of the obsidian samples as they were
being prepared for analysis in the spectrograph did not reveal any notable
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87
differences in appearance which seemed trustworthy as criteria for sorting
the samples. When it became clear, however, that the obsidians did fall
into several distinct groups, based upon x-ray fluorescence analysis, a more
detailed inspection of the samples in hand specimen was clearly advisable.
Accordingly, the first 55 La Venta surface samples run on the spectrograph
were examined under reflected artificial light and on a light table, and any
pertinent observations recorded. In addition, all samples found by x-ray
fluorescence to lie outside the compositional range of the three dominant
(86% of the La Venta surface sample) groups A, B, and C, and all excavated
samples catalogued with Roman numerals were examined in a similar manner.
The results are summarized in Table 1.    The three dominant types A, B. and
C have consistent characters, type A being a distinctive green color, type B
being a generally uniform smoky gray, and type C being light gray with a
definite tan tint with a dense tan to black internal flecking. More signif-
icant, however, is the fact that type D samples have a darker, more irregular
streaky (inhomogeneous?) appearance than type B. supporting the narrow dis-
tinction between the two types observed chemically, and the fact that samples
belonging to the rather broad group designated type E have a consistent
greenish-yellow tint to their light gray body color, supporting their identi-
fication as a valid obsidian type. Of the 12 samples (not including No. 1)
not falling within one of the five major chemical types, numbers 54, XVI, and
XVII in one group and numbers 70, 117, VII, and IX in another group, are most
like type C obsidians in hand specimen, and numbers 3 and 52 are most like
type B in hand specimen.   Samples numbered 4, 5, and 89, although generally
similar to each other in that they are dark gray and finely flow banded or
mottled, do not have definite similarity to any other observed groups.
At this time any statistical statement regarding the obsidian types in
Mesoamerica must be in terms of the La Venta surface samples or in terms of
all samples analyzed (including the La Venta surface samples) since only thus
is there a sufficiently large sampling. A summary of the finding of this
study is given on page 88. It is notable that by means of the non-destruc-
tive x-ray fluorescence rapid scan method 94.0% of the available La Venta
surface samples and 92.6% of all samples analyzed may be assigned to one of
five major chemical types; 86.0% and 82.4%, respectively, belong to the three
major types.   Figure 3 is a summary plot of the samples belonging to the
five major chemical groups.    No chemical types were observed among the exca-
vated samples which were not represented in the La Venta surface sampling;
however, type E of the La Venta surface obsidians was not observed among the
excavated samples. Both samples from Tlatelolco burials are of type A
(Pachuca).  Of the 10 Tres Zapotes samples, 6 are of type D, 2 of type B.,
and 2 are similar to La Venta surface sample 54 in composition. The single
Comalcalco sample (No. IX) is similar in composition to La Venta sample VII
and two La Venta surface samples, numbered 70 and 117. Sample VII is the
only excavated La Venta sample not belonging to one of the three dominant
types A, B, or C.
88
La Venta Surface Samples  11      All Samples
*11
Obsidian  || No. of     I  Per cent     11     No. of    I  Per cent
Type     |  Samples   |  of Total     11     Samples   |  of Total
A       I|      24       |     15.9
B       ||      62       |     41.0
C       11      44      1      29.1
D       ||       3      |       2.0
E       ||       9       |      6.0
Other     1l        9      1       6.0
29        1      16.5
.I           66        1      37.5
II           50        1       28.4
II             9       1        5.1
1H             9       1        5.1
II           13        1        7.4
Total           151     |    100.0                  176      |    100.0
Tables 2 through 6 summarize the data for the 163 samples belonging to
each of the five major obsidian groups, and Table 7 presents the same type
of data for the remaining 13 samples and the 3 geologic samples (potential
sources), generally similar samples being grouped for comparison. The units
used are chart divisions measured from the spectrograph charts, one division
being equivalent to a counting rate of 20 counts per second. The columns
entitled Rb/X, Sr/E, and Zr/s are the values used to plot the composition of
each sample on the ternary diagrams. The samples are identified by number
in Appendix I, arabic numerals being used for La Venta surface samples and
Roman numerals for the excavated La Venta samples and those-from other
localities. Included in each table are average values (in chart divisions)
for Rb, Sr, Y, Sr, and Nb for that obsidian type, with an approximate value
in parts per million (by weight) for each element based upon comparison with
U.S. Geological Survey standard granite G-1. These values are uncorrected
for matrix mass absorption, but are expected to be accurate within a few per
cent of the amount present. Also included in Table 2 are measurements taken
on green obsidians from northwesternmost Nevada (Hu X-1 and Hu X-2) which
confirm their general similarity with the Pachucan green obsidians but also
reveal significant differences in the Y, Zr, and Nb concentration levels.
In conclusion, it can be said that the x-ray fluorescence rapid scan
technique holds great promise in characterizing Mesoamerican obsidians and
thereby contributing to the solution of certain basic archaeological prob-
lems. In cases in which the rapid semi-quantitative determination of Rb,
Sr, and Zr, plus Y and Nb, doesnot provide adequate resolution between
obsidian types, measurement of the concentrations of other elements may be
useful. The desirability of further sampling at a number of archaeological
89
sites, and equally important, the collection of geologic source obsidian, is
indicated in order to further define other obsidian chemical types and to
establish the sources and distribution of Mesoamerican obsidians.
Initial work on Mesoamerican obsidians by Weaver and Stross (1965) was
successful in demonstrating that obsidian from Pachuca (i.e. Cerro de
Navajas, Hidalgo) was traded as far south as the La Venta site in the state
of Tabasco, but the archaeological sample was collected from the surface
and could not be dated. Excavations at La Venta in July, 1967, and January-
February, 1968, produced 12 small obsidian blades ("razors"; samples Nos.
1-VII, XXI-XXV). All of these, without exception, were recovered from
refuse or constructions of the La Venta period (Middle Pre-Classic) and
dated at this site in the time span 1000 B.C. - 600 B.C. (cf. Berger, Graham
and Heizer 1967). Since three of these are of Type A obsidian from Pachuca,
we can be certain of the fact that obsidian from the Mexican highland was
being traded to southeastern Mexico in the Middle Pre-Classic. Drucker
(1952:145) observes that he found no green obsidian in the test pits and
stratigraphic trenches dug by him at La Venta in 1941. We do not know how
to explain this, since several of our pits were in areas immediate to those
where he had dug some twenty years earlier. Obsidian samples from highland
01mec sites such as Tlapacoya, Tlatilco, Las Bocas, Chalcatzingo, and others,
when analyzed by the method employed here might provide us with information
on the intensity of contacts between these various sites.
The Ixtepeque (Guatemala) source is apparently not represented at La
Venta, unless we accept the general similarities of La Venta samples 4 5,
and 89 to Ixtepeque obsidian as supporting this. However, this is not sur-
prising in view of the fact that these two spots lie 380 airline miles apart.
At the same time, it is puzzling to find that the El Chayal source in Guat6-
mala (Coe and Flannery 1964) may have provided the material for samples VII,
70, and 117 (from La Venta) and IX (from Comalcalco). In view of the Olmec
presence in Salvador (Boggs 1950) and southeastern Quetzaltenango, Guatemala
(Thompson 1943:III,fig. a), it would not be surprising to find some indica-
tion of material interchange between the Veracruz-Tabasco Olmec area and the
Guatemala-Salvador region.
A single source, not now identified, supplied obsidian both to the La
Venta and Tres Zapotes sites as judged from samples XVI and XVII (Tres
Zapotes) and No. 54 (La Venta).
One obsidian type (E) known from surface artifacts at La Venta was not
found in excavations. This obsidian may either date from post-La Venta
phase times at the La Venta locality or, since it is represented by only 9
specimens, it may be a rare type which we did not encounter in our limited
investigations of 1967 and 1968.
90
Of the five major source types identified (ABCDE) only type A is
now locatable. Type B obsidian is the most abundant at La Venta, type C
is next most common, and type A is in third place. The greatest need now
is to have samples of source obsidians with which to correlate La Venta
artifacts.
APPENDIX I
LOCALITY DESCRIPTIONS OF SAMPLES
1      Surface obsidian samples, mainly fragmentary flake blades, collected
through   from La Venta site in February, 1968.    Sequential numbers assigned
151     as specimens were run on x-ray spectograph.
I.        From refuse deposits west of La Venta pyramid.    Collected in July,
1967, by R. F. Heizer and P. Drucker.   Test Pit No. 3, d. 8-16 in.
II.       Same as I.
III.      Same as I.
IV.       Stirling Group southeast of La Venta pyramid.    Specimen found in
gray gumbo packing of Drain No. 1. Collected February, 1968, by
NGS-UC expedition.
V.         Same as IV.
VI.       Refuse deposits lying on top of large rectangular platform con-
struction (shown on site map in this volume as "Great Platform")
near southwest corner of the south platform of the La Venta
pyramid. Test Pit No. 2, level 3 (d. 40-60 cm.). Dates from La
Venta phase. Collected January, 1968, by NGS-UC expedition.
VII.      Same location as VI.   Test Pit No. 1, level 8 (d. 140-160 cm.).
VIII.     Tlatelolco, Mexico.   Flake blade found in mouth of Burial No. 1.
Assignable to Aztec II-III period on basis of associated pottery.
Collected by UC research group on February 15, 1968.
Ux.       Comalcalco, Tab., Mexico.   Surface obsidian chip collected
February 7, 1967.
X.         Number not used.
91
XI - XX   Ten obsidian samples recovered by P. Drucker from a test pit
excavated in the cutbank of the Arroyo Hueyapan at the locus
of his earlier Trench 26. Sequential numbers assigned as run
on x-ray spectograph.
XXI.      La Venta site.   Test Pit 1968-1, level 6 (d. 100-120 cm.).
XXII.     La Venta site.   Test Pit 1968-2, level 7 (d. 120-140 cm.).
XXIII.    La Venta site.   Test pit 1968-2, level 8 (d. 140-160 cm.).
XXIV.     La Venta site.   Test Pit 1968-2, level 5 (d. 80-100 cm.).
XXV.      La Venta site.   Test Pit 1968-5, level 7 (d. 120-140 cm.).
XXVI.     Tlatelolco, Mexico. Flake blade found in mouth of Burial 2.
Assignable to Aztec II period on basis of associated pottery.
Collected by UC research group on February 14, 1968.
Table 1. Summary of the appearance of five major
obsidian types (in hand specimen)
Type A    Distinct olive green body color (to greenish-black in thicker sec-
tions). Commonly shows golden internal reflections from parallel
discontinuous planes (incipient cracks?). Occasionally golden re-
flections are on a very fine (powdery) scale. Generally smooth
fracture surfaces of high lustre. Fine cracks often visible running
in curves perpendicular to conchoidal fracture rings or undulations.
Occasionally small tan spherules or trains of spherules are visible.
Type B    Light gray, dark gray, to nearly black body color.    Clear uniform
smoky-gray color generally characteristic. Occasional faint darker
gray streaking visible in light gray body color. Surface highly
lustrous to somewhat greasy; occasionally faintly irridescent.
Diverging curved cracks observed occasionally. Occasional spots;
vesicles rare.
Type C    Light gray with distinct tan tint, particularly in thicker sections.
Dense flecking of fine tan, brown, to black spots is characteristic.
Areas of shadowy gray streaking or banding due to concentration of
fine spots is common, more obvious when viewed parallel to plane of
spots. May be very light gray to clear in thinnest sections. Sur-
face usually greasy in lustre due to roughness related to dense
flecking. Lustrous surface only when flecking is on finest scale.
Type D    Dark gray to black with streaky appearance.    Dense irregular mot-
tling of dark gray in lighter gray background. Surface shiny to
pitted (with a greasy lustre).
Type E    Light smoky-gray with greenish-yellow tint.    Clear to greenish-gray
in thinner sections. Faint banding on fine scale. Very fine spot-
ting gives dusty internal appearance; occasional larger spots of
rust coloring. Faint banding becomes more distinct on rotation of
sample to certain orientations. Surface generally highly lustrous,
occasionally pearly.
93
Table 2.
Sample
Number Rb
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
146
III
VIIi
XXI
Xxv
XXVI
23.5
24.0
24.0
24.0
25.0
25.5
16.5
21.0
23.0
21.0
24.5
22.5
23.0
23.5
23.0
21.0
23.5
21.5
22.0
22.0
22.0
22.0
23.0
22.0
25.5
23.0
23.0
23.0
24.5
Sr
1.0
0.5
0.5
0.5
1.0
1.0
3.0
0.5
0.5
0.5
0.5
1.5
0.5
1.0
0.5
1.0
0.5
0.5
0.5
0.5
1.0
1.0
0.5
1.5
0.5
1.0
1.0
1.0
1.5
Summary of Data for Obsidians of TYPE A
(1.0 equivalent to 20 counts per second)
y
15.0
17.5
16.5
14.5
16.5
14.5
14.5
14.5
14.0
15.0
15.5
15.0
16.0
15.0
15.0
16.5
15.0
16.5
17.5
15.0
15.0
15.0
15.0
15.0
15.5
16.0
16.5
16.0
15.0
Zr
146.0
146.5
150.0
149.0
152.5
151.5
114.5
146.5
145.0
144.0
151.5
144.5
144.0
145.0
146.5
140.0
145.0
146.5
152.5
140.0
140.0
140.0
139.0
139.5
150.5
147.5
141.5
140.0
142.5
Nb Z(Rb, Sr, Zr) Rb/?
10.5
13.0
14.0
14.0
17.0
14.5
19.5
17.5
13.5
12.5.
13.0
14.0
13.0
12.5
14.0
13.0
13.0
10.5
13.5
12.5
12.5
12.5
11.5
13.5
15.5
15.0
15.0
13.5
15.0
170.5
171.0
174.5
173.5
178.5
178.0
134.0
168.0
168.5
165.5
176.5
168.5
167.5
169.5
170.0
162.0
169.0
168.5
175.0
162.5
163.0
163.0
162.5
163.0
176.5
171.5
165.5
164.0
168.5
.138
.142
.137
.138
.140
.142
.122
.126
.136
.128
.140
.134
.137
.139
.135
.130
.139
.128
.126
.135
.136
.135
.142
.135
.143
.134
.139
140
.145
Sr/i
.oo6
.003
.003
.003
. oo6
4.007
.022
.005
.oo4
.005
.003
* 009
4003
. oo6
.003
. oo6
.003
.003
.003
.003
.003
. oo6
.003
.009
.003
.oo6
. oo6
. oo6
. 009
Zr/.r Total
.856
.855
.860.
.859.
.854
.851
.857
.869
.860
.867
.857
.858
.860
.855
.862
.864
.858
.869
.871
.862
.861
.859
.855
.856
.853
.86o
.855
.854
.846
1.000
1.000
1.000
1.000
1.000
1.000
1.001
1.000
1.000
1.000
1.000
1.000
1.000
1.000
1.000
1.000
1.000
1.000
1.000
1.000
1.000
1.000
1.000
1.000
.999
1.000
1.000
1.000
1.000
0.83   15.40  144.15  13.54
7     124   1164
109
(La Venta surface samples)
Standard: G-1
-For comparison the following data are given for samples from northwest Nevada:
HU X-1 23.0
HU X-2 24.0
0.5   11.0   85.0
0.5   12.5   90.0
5.5 108.5 .212
5.5 114.5 .210
.005  .783 1.000
.004  .786 1.000
Ave rag e
Of 24
Ppm
22.63
251
94
Sample
Number Rb
2
30
31
34
37
42
47
49
50
53
-57
58
60
61
63
64
67
71
74
79
80
81
82
84
85
86
87
93
94
96
97
98
99
100
101
102
103
io6
io8
109
110
113
114
115
116
118
120
122
124
126
Table 3. Summary of Data for Obsidians of TYPE B
(1.0 equivalent to 20 counts per second)
19.5
19.0
18.0
18.5
20.5
20.5
21.5
20.5
20.5
23.0
20.0
20.0
17.0
18.0
20.5
20.0
19.5
21.5
19.0
19.0
18.0
20.5
19.5
20.5
20.0
20.0
19.0
18.5
19.0
18.5
19.0
19.0
19.0
17.0
20.5
P0.5
20.5
19.0
18.5
20.5
22.0
21.0
19.5
20.0
19.0
20.5
20.0
19.0
19.0
22.0
Sr
1.0
1.0
1.0
2.0
1.0
1.0
1.0
1.0
1.0
0.5
2.0
1.0
1.5
1.5
1.5
0.5
1.0
0.5
1.0
0.5
0.5
1.0
1.5
1.0
1.5
1.5
1.5
0.5
0.5
2.0
1.5
1.5
1.5
1.5
1.5
1.5
.1.0
1.0
0.5
1.0
2.0
1.5
1.0
0.5
0.5
1.5
1.0
2.0
1.5
2.0
y
6.o
7.0
8.0
10.0
6.o
6.0
6.0
8.0
7.5
7.0
9.0
9.0
9.0
6.0
9.0
7.0
7.5
7.5
7.5
8.0
6.o
8.0
5.5
7.5
8.5
6.5
8.0
8.o
7.5
7.0
7.0
8.0
7.5
6.5
9.5
7.0
6.5
6.o
6.5
8.5
8.o
7.5
7.0
7.0
6.5
7.0
7.5
6.5
8.0
8.o
Zr
33.0
30.5
31.5
33.0
34.o
32.0
33.0
32.5
32.5
34.5
32.0
32.5
28.5
30.5
31.0
31.0
31.5
32.5
30.5
32.0
29.5
31.0
29.5
31.0
31.5
30.0
30.5
31.5
31.0
27.0
31.0
30.0
30.0
29.0
31.5
31.0
30.5
31.0
29.5
32.0
30.5
31.5
31.0
31.5
30.5
31.5
30.0
28.5
31.0
33.0
Nb ?(Rb, Sr, Zr) Rb/i
7.5
7.5
7.0
6.5
6.o
8.5
7.5
8.o
6.5
8.5
7.5
7.0
7.5
7.0
6.5
6.5
7.5
8.5
4.o
7.0
6.5
6.5
6.5
6.o
6.5
8.o
7.0
7.5
7.0
5.5
7.5
7.0
6.5
6.o
7.0
8.5
6.5
7.5
8.0
8.0
6.5
7.0
7.5
7.5
6.5
7.0
6.5
6.5
5.5
6.5
53.5
50.5
50.5
53.5
55.5
53.5
55.5
54.0
54.o
58.0
54.o
53.5
47.0
50.0
53.0
51.5
52.0
54.5
50.5
51.5
48.0
52.5
50 5
52.5
53.0
51.5
51.0
50.5
50.5
47.5
51.5
50.5
50.5
47.5
53.5
53.0
52.0
51.0
48.5
53.5
54.5
54.0
51.5
52.0
50.0
53.5
51.0
49.5
51.5
57.0
.364
.376
.356
.346
.369
.383
.387
.380
.380
.394
.370
.374
.362
.355
.390
.388
.375
.391
.376
.369
.375
.390
.386
.390
.377
.388
.373
.366
.376
.389
.369
.376
.376
.358
.383
.388
.394
.377
.381
.383
.404
.389
.379
.385
.380
.381
.392
.384
.369
.386
Sr/E
.019
.020
.020
.038
.018
.019
018
019
019
.010
.037
.019
.034
.032
.024
.010
.019
.011
.020
.010
.010
.019
.030
.019
.028
.029
.029
.010
.010
.042
.029
.030
.030
.032
.028
.031
.019
.016
.010
.019
.037
.028
.019
.010
.010
.031
.020
.040
.029
.035
Zr/Z
.617
.604
.624
.617
.613
.598
.595
.602
.602
.596
.593
.607
.603
.613
.585
.602
.6o6
.598
.604
.621
.615
.590
.584
.590
.594
.583
.598
.624
.614
.568
.602
.594
.594
.610
.589
.582
.587
.607
.608
.598
.560
.583
.602
.606
.61o
.588
.588
.576
.602
.579
Total
1.000
1.000
1.000
1.001
1.000
1.000
1.000
1.001
1.001
1.000
1.000
1.000
.999
1.000
.999
1.000
1.000
1.000
1.000
1.000
1.000
.999
1.000
.999
.999
1.000
1.000
1.000
1.000
*999
1.000
1.000
1.000
1.000
1.000
1.001
1.000
1.000
.999
1.000
1.001
1.000
1.000
1.001
1.000
1.000
1.000
1.000
1.000
1.000
95
Table 3.  continued
Sample
Number Rb
127
129
131
133
134
135
142
143
145
147
148
150
VI
XVIII
xx
XXIV
20.0
19.5
21.0
19.0
19.5
19.5
19.0
22.0
19.0
21.0
19.5
21.5
20.0
19.5
19.5
17.5
Sr
1.0
2.0
0.5
1.5
0.5
2.0
2.0
1.0
2.0
1.5
1.5
1.5
1.5
2.0
1.5
1.0
y
6.5
7.0
6.5
7.5
7.5
8.0
9.0
9.0
6.o
7.0
7.5
6.5
8 5
6.5
7.0
6.5
Zr
30.5
27.0
34.0
30.0
31.5
32.0
31.0
34.0
27.5
30.5
30.5
30.5
34.5
31.5
28.5
30.5
Nb E(Rb, Sr, Zr) Rb/r
7.5
7.0
8.5
7.0
7.0
7.0
7.0
6.5
7.5
7.0
7.5
9.0
9.0
7.0
7.0
7.0
51.5
48.5
55.5
50.5
51.5
53.5
52.0
57.0
48.5
53.0
51.5
53.5
56.o
53.0
49.5
49.0
.388
.403
.377
.376
.379
.364
.365
.386
.392
.396
.379
.402
.357
.368
.394
.357
Sr/r
.019
.042
.009
.030
.010
.037
.038
.o18
.041
.028
.029
.028
.027
.038
.030
.020
Zr4.  Total
.592
.556
.613
.594
.612
.598
.596
.596
.567
.575
.592
.570
.616
.594
.576
.622
.999
1.001
.999
1.001
1.001
.999
.999
1.000
1.000
.999
1.000
1.000
1.000
1.000
1.000
.999
Average 19.77
of 62
1.23   7.38  31.04  7. o6
60     251      57       Standard: G-1
ppm   220     11
96
Tabl1e 4. Sur mar of Data for Obsidians of TYPE C
(1.~0equivalent to 20 counts per second)
Sample
Number Rb
32
33
35
36
38
39
40
43
44
45
46
48
51
55
59
62
66
68
69
72
73
76
77
91
92
95
104
105
107
111
112
119
121
125
128
130
132
136
137
138
139
141
144
149
I
II
IV
V
XXI I
XXIII
Ave rage
of 44
14.5
13.5
13.5
14.0o
12.5
14.0o
13.5
14.5
14.5
12.5
14.0o
13.0
12.0
15.0
12.5
13.5
14.5
13.0
13.5
12.0
13.5
13.0
12.5
13.5
13.0
13.5
13.0
12.5
13.0
13.0
13.0
13.5
13.5
13.0
14.5
13.5
11.5
13.0
12.0
14.0o
13.0
15.0
12.5
14.0o
14.0o
13.5
15.0
14.0o
14. o
14. o
13.33
Sr
Y
22.0
24.5
24.0o
24.0o
21.5
26.0o
23.0
26.5
26.0o
22.5
24.0o
26.5
24.0o
25.0
25.5
22.0
23.5
24.5
24.0o
25.0
22.5
24.0o
24.5
25.5
23.0
23.0
24.0o
24.0o
21.0
22.5
23.5
23.0
23.5
23.0
25.0
24.0o
22.0
21.5
22.0
23.0
24.5
24.5
21.5
23.5
25.0
25.0
26.5
26.0o
24.0o
22.5
23.69
2.5
3.5
2.0
1.5
2.5
3.5
2.0
2.5
2.0
2.5
1.5
1.5
4.0o
4.0o
4.0o
1.5
5.0
2.5
2.5
3.0
4.0o
3.0
2.5
2.0
3.0
3.0
2.0
3.0
2.5
2.5
2.5
3.0
3.0
3.5
2.0
3.0
2.5
2.5
1.0
3.0
3.5
2.5
2.5
1.5
0.5
2.5
3.0
2.5
2.5
1.5
2.67
Zr
Nb I(Rb, Sr,,Zr) Rb/2i
16.0o
15.5
17.0
16.5
15.0
14.0o
15.0
17.0
16.0o
17.0
18.0o
15.5
18.0o
19.0
16.0o
16.0o
17.5
15.5
16.0o
17.0
12.0
18.0o
14.5
17.5
14.0o
15.0
15.5
16.0o
15.5
14.5
17.0
17.5
17.5
14.0o
16.0o
16.5
14.5
17.5
15.0
15.0
16.0o
16.5
15.5
17.0
16.5
19.5
15.0
15.5
16.09g
1.5
1.5
1.0
0.5
0.0
3.0
0.5
0.5
1.0
2.0
2.5
0.5
1.0
1.5
3.5
0.5
2.0
2.5
1.0
1.5
3.0
2.5
2.5
1.5
2.5
2.0
3.5
2.0
2.0
2.5
2.0
1.5
2.5
3.0
2.0
2.0
2.0
2.5
1.0
2.5
2.0
2.0
1.0
2.5
2.0
2.5
3.0
1.5
2.0
1.78
52.5
53.5
54.5
54.5
49.0o
54.0o
51.5
58.0
56.5
52.0
56.0o
55.0
56.0o
54.5
54.0o
53.5
55.0
52.5
52.0
54.0
49.0
57.0
50.5
54.0
51.0
51.5
49.5
51.5
52.0
51.0
54.0o
53.5
57.0
51.5
49.5
51.0
48.5
54.5
52.5
54.5
50.0
54.0
54.5
55.5
58.0
59.5
53.0
52.0
.276
.252
.248
.257
.255
.259
.262
.250
.257
.240
.250
.236
.231
.255
.226
.245
.269
.244
.245
.127
.256
.241
.256
.237
.257
.250
.255
.243
.263
.252
.250
.264
.252
.243
. 254
.262
.232
.255
.247
.257
.248
.275
.250
.259
.257
.243
.259
.235
.264
.269
S r/zi Zr/,i Total
.419
.458
.440
.440
.439
.481
.447
.457
.460
.433
.429
.482
451
:434
.452
.404
.435
.462
.436
.477
.436
.444
.500
.447
.455
.426
.471
.-466
424
:437
.452
.448
.437
.430
.439
.466
.444
.422
.454
.422
.467
.450
.430
.435
.459
.450
.457
.437
.453
.433
.305
.290
.312
.303
.306
.259
.291
.293
.283
.327
.321
.282
.319
.311
.321
.351
.296
.295
.318
.295
.308
.315
.244
.316
.287
.324
.275
.291
.313
.311
.298
.287
.311
.327
.307.
.272
.323
.324
.299
.321
.286
.275
.320
-306
.284
.306
.284
.328
. 283
.298
1.000
1.000
1.000
1.000
1.000
.999
1.000
1.000
1.000
1.000
1.000
1.000
1.001
1.000
.999
1.000
1.000
1.001
.999
.999
1.000
1.000
1.000
.999
1.000
1.001
1.000
1.000
1.000
1.000
.999
1.000
1.000
1.000
1.000
.999
1.001-1
1.000
1.000
1.001
1.000
1.000
1.000
1.000
.999
1.000
1.000
1 * 000
1.000
ppm  148  212  ~~~ ~~22  130  14StnadG1
PPM   148    212
Standard: G-1
97
Sample
Number Rb
Table 5. Summary of Data for Obsidians of TYPE D
(1.0 equivalent to 20 counts per second)
Sr
y
Zr
Nb 4(Rb, Sr, Zr) Rb/i Sr*j
Zr/zj Total
3.0
2.0
3.5
5.0
3.0
2.5
4.0
3.5
2.0
51.0 .324
48.5  .341
48.5  .350
47.5
51.0
50.5
51.0
51.0
48.5
.326
.343
.327
.333
.333
.330
. o88
.088
.082
.074
.o69
.079
.095
.078
.082
.588  1.000
.571  1.000
.567   .999
.600
.588
.594
.571
.588
.588
1.000
1.000
1.000
.999
.999
1.000
4.33    4.83  28.33   2.83
4.11
4.33  29.00  3.17
35      234     26
6
56
151
XI
XII
XIII
xIv
xv
XIX
Average
of 3
16.5
16.5
17.0
15.5
17.5
16.5
17.0
17.0
16.0
16.65
4.5
4.5
4.0
3.5
3.5
4.0
5.0
4.0
4.0
4.5
5.0
5.0
4.0
3.0
3.0
5.0
4.0
5.5
30.0
27.5
27.5
28.5
30.0
30.0
29.0
30.0
28.5
Average
Of all 9
PPM    185    37
Table 6. Summary of Data for Obsidians of TYPE E
(1.0 equivalent to 20 counts per second)
12.5
12.5
12.5
12.5
11.5
13.0
12.5
13.0
12.0
Sr
3.5
4.0
6.o
2.5
3.5
3.5
5.5
4.0
4.0
y
3.0
2.5
2.0
2.5
1.5
2.5
2.0
3.5
2.5
Zr
8.0
7.5
8.0
7.0
8.0
9,0
7.0
8.0
8.5
Nb Z(Rb,Sr,Zr) Rb/i
2.0
1.5
2.5
3.0
4.0
3.5
5.0
2.5
2.5
24.0
24.0
26.5
22.0
23.0
25.5
25.0
25.0
24.5
.521
.521
.472
.568
.500
.510
.500
.520
.490
Sr/z
.146
.167
.226
.114
.152
.137
.220
.160
.163
Zr/,?  Total
.333
.313
.302
.318
.348
.353
.280
.320
.347
1.000
1.001
1.000
1.000
1.000
1.000
1.000
1.000
1.000
12.44
4.o6   2.44  7.89   2.94
20      64      24
98
Sample
Number Rb
41
65
75
78
83
88
90
123
140
Average
of 9
PPM    138    36
Standard: G-1
99
Table 7.
Sample
Number Rb
Summary of Data for Obsidians Not Belonging to
Five Dominant Types
(1.0 equivalent to 20 counts per seaond)
Sr
y
Zr
Nb Z(RB,Sr,Zr) Rb/4
Sr/'t
Zr/j Total
C1        l1
17.5
17.5
(Cf El
16.5
17.0
18.5
17.5
9.5
7.5
11.0
2.5
3.0
Chayal)
19.0
19.0
21.0
19.5
1.5  11.0
2.5   9.5
3.5  14.0
3.0  17.5
4.0  18.5
3.0
2.5
4.0
2.5
15.0
16.0
15.5
15.5
(Cf Ixtepeque)
4    14.0   16.0    3.0   20.5
5    16.5   18.5    2.5   22.5
89    11.5   22.5    3.5   31.0
Pc1huca (Cf Type A, Table 2)
3.0   32.0
2.0   27.5
2.0   40.0
* 359
.382
.375
3.5   37.5 .467
3.5   39.0 .449
3.5
3.5
CD-5
1.0
1.5
1.5
3.0
50.5
52.0
55.0
52.5
50.5
57.5
65.0
*327
.330
.336
.333
.277
.287
.177
22.5  0.5
15.5  137.5   12.5  160.5  1140
.003  .857 1.000
El Chayal
15.5   16.5
2.5  14.5
2.0   46.5 .333
.355   .312 1.000
Ixtepeque
clear 12.5
17.5
3.0  24.0
1.5   54.0  .231
.324   i444   .999
flow- 13.0
banded
21.5
2.5  24.5
1.0   59.0  .220   .364   i 415  .999
U. S. G. S. Standard Granite G-1
19.5
20.0
20.0
Average 19.8
G-1
27.0
29.0
28.0
28.0
2.0  25.5
1.5  27.5
2.5  25.0
2.0  26.0
Ppm     220    250
1    "'1
< 1
11.5
10.5
15.0
< 2
3
52
70
117
VII
Ix
.297
.273
.275
.o67
.077
.376
.363
.382
.371
.317
.322
.346
.344
.345
.350
.467
.474
.297
.308
.282
.295
.406
.391
.477
1.000
1.000
1.000
1.001
1.000
1.000
1.0031'
1.000
.999
1.000
1.000
1.000
1.0
4.5
2.5
2.7
13    210      20
100
Bibliography
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1967    A Reconsideration of the Age of the La Venta Site.    Contribu-
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1950    "Olmec" Pictographs in the Las Victorias Group, Chalchuapa
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1967    "Finger-Printing" of Obsidian and Pumice from the Western
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