University of Virginia Library

Section B

UTILIZED MINERALS AND ROCKS AND THEIR SOURCES

By Douglas Osborne

Specimens of the following materials were obtained from Bc 50-51:
red shale (pendant, 2 smoothed pieces, 2 drilled pieces); flinty chalcedony
(hammerstones and flakes); chalcedony, moss agate (scraper);
grey chalcedony (point); white chalcedony (point); obsidian (flakes,
knives, points); turquoise (beads,[15] pendants,[16] drilled and smoothed
pieces); quartzite (black and yellow), (polishing stones, hammerstones);
calcareous sandstone or siltstone[17]
(concretional fragments,
beads, pot covers, sandal lasts or weaving spacers, smoothers, pendant?);
kidney iron ore (small oolitic piece, bird fetish?,[18] yellow ochre,
red ochre, gilsonite (part of a ring),[19] malachite, azurite.

In the endeavor to determine the incidence of occurrence of the
various minerals used for chipped artifacts, the spalls, etc., were collected,
level by level, from the various sections of the refuse mound in
the same manner as were the potsherds. They were examined and
separated and percentages taken. These percentages were then
plotted by levels by Margaret Latady. In no case was material recovered
from levels 1-2. The total number of specimens identified was 430.

The results may be summarized briefly. Chalcedony and chalcedonic
wood or petrified wood outstripped all of the other stone materials
in actual number of spalls and in percentages. Petrified wood and
chalcedony were of approximately equal quantity in 8 of the 24 samples
in which they occurred together; they were unequal, then, in 16 of
these occasions. In only 3 of the 16 instances that the two materials

occurred unequally together were chalcedony pieces the more numerous.
In other words, by far the greater amount of cryptocrystalline quartz
used (and that material was the material par excellence) was obtained
from opalized or petrified wood. Inasmuch as it was rather difficult,
in many cases, to distinguish between flakes of petrified wood and flakes
of otherwise formed chalcedony, there must be a good deal of admixture
between the two. That is, many a fragment of petrified wood might
have been called chalcedony, pure and simple, and vice versa. In fact,
I am inclined to believe that the two are of one series. That is, they
were used interchangeably and much of the chalcedony had petrified
wood as a source.

Obsidian, which always occurs sparingly, is confined, in general,
to the upper levels. Neither the jaspers nor quartzites were used extensively.
The highest percentage of the former in any sample was 11
per cent, of the latter 7 per cent.

In the Chaco Wash proper, there are few igneous or metamorphic
pebbles found. There were, however, two sources[20] of these discovered
in the wash. One of these sources was directly below the ruin of
Peñasco Blanco. Here were found a few pebbles of coarse quartzite
in a cemented, gravelly deposit. These, so far as found, were unsuited
for making any of the finer implements. Their only use could have
been in the form of hammerstones or other rough implements. The
same is true for a deposit in the arroyo one-fourth mile NW of Mesa
Fahada. Here, too, a gravelly cemented formation (probably a calcitic
cement) displays a number of rough, igneous and or metamorphic
pebbles. This formation is lenticular in the higher walls of the arroyo,
most prominent and in larger beds rather than lenses in the lower third.
It calls to mind the Mortar Beds[21] of the Pleistocene. Because the
deposit is well cemented it stands out in ridges on the floor of the
arroyo. The contained, rolled, igneous material is unfit for any of the
finer tools of the aboriginal inhabitants of the Canyon. The deposit
should be examined more thoroughly and searched for more carefully
between Mesa Fahada and Peñasco Blanco (if I may assume that the
two outcrops are of the same deposit) as it might have no small bearing
on the recent geological history of the canyon.

Examination of the tops of the South Mesa and the Chacra Mesa
and counts made of the gravels on them, investigated by Dr. Malcolm
Bissel, showed a high percentage of quartzites. On South Mesa there
were six light yellow quartzites to one of a darker quartzite. On the
Chacra, again, quartzite was the only rock of importance; all of the
occurrences were in the form of rounded, water-worn pebbles. A count
of four square feet above the Escavada Wash to the north of Pueblo

Bonito in the area of the exposure of the Pictured Cliffs sandstone
showed the following:

         

Petrified Wood	20 pieces
Chalcedony (agate, etc.)	6 pieces
Quartzite	6 pieces
Brown Jasper	6 pieces
Red Jasper	2 pieces

This corresponds rather closely with the situation shown in the graphs
of the incidence of the spalls found in the stratigraphy tests taken of
the refuse mound Bc 50-51. There is an obvious proportional relationship
between the series.

The petrified wood found in the stratigraphy levels corresponds,
superficially, to some found in the Escavada Wash. The two appear
identical when examined megascopically. This petrified wood probably
comes from above the Ojo Alamo outcrop—possibly in the Paleocene or
Eocene exposures. The petrified wood found in the Kirtland shale
(Cret.) and in the Ojo Alamo (Cret.) sandstone is lighter in shade,
more granular and friable than that of the wash and is certainly not
of the best type for implements, whereas that of the Escavada and, of
course, that of the stratigraphy tests is highly adaptive to the Indian
chipping technique. The tabular deposits of silicon dioxide found in
logs of petrified wood were used extensively for implements, and were
probably the source of much of the "chalcedony" found in the ruins.[22]

In general the obsidian of Chaco Bc 51, when compared with some
from Jemez (Unshagi), showed a more fibrous appearance. This
fibrousness is probably an expression of the flow; impurities are spread
or dragged out along the same plane. The true obsidians are about
equally transparent but that of Jemez seems to carry less impurities.
One can only say definitely, concerning the source of the Chaco obsidian,
that it did not come from the same flow as did the Unshagi piece.

Following information which Dr. W. W. Hill obtained from a
Navaho informant, a search was made for common salt (NaCl) in
Escavada Arroyo and throughout the region. Halite was not found,
but many deposits of impure magnesium sulphate (Epsom salts) were
located. In a small cave on South Mesa, a cave in the north wall of the
canyon, an arroyo tributary to the Escavada, which branches to the
west along the face of the exposure of Ojo Alamo; in the Escavada,
about 300 yards up the wash from the bridge on the Chaco Canyon-Aztec
road, are some of the many places where Epsom salts have been
deposited.

Probably some of the amorphous gypsum found in the ruins was

formed by a disintegration of the crystals of selenite which were carried
into the rooms by the inhabitants. Pieces of alabaster are not
infrequently found in the canyon. One was picked up from the foot of
the north wall of the canyon near Yellow House. It comes, I believe,
from the Chacra sandstone itself.

The question of jet, or possibly cannel coal, must await the exploration
of Upper Coal Creek (Sternberg). Probably all of the so-called
jet has been gilsonite.

It is not possible to state the provenience of the turquoise found.
Only after a thorough mineralogical study of La Para, Cerrillos,
Reserve, and the Chaco turquoise, can we be sure where the turquoise
found in the Chaco came from. It is probably Cerrillos.

Ochre and rouge are notoriously plentiful throughout the Navaho
Reservation. In fact, the Navaho, according to two Jemez Indian informants,
trade colored earths to the Pueblos today and profit from a
virtual monopoly of some of the brighter shades. A number of deposits
of ochre and rouge were located during the survey. Rouge is prominent
in the Allison member of the Chacra sandstone, on the south side of
Mesa Fahada, and on the south and west faces of Chacra Mesa. While
other deposits exist along the walls of the canyon and to the south in
the Red Hills, the best and most varied exposures of colored earths occur
on the extreme jutting point of the west walls of the re-entrant in which
are the Wetherill coal mines. Here is vermillion, yellow, orange, and a
deep purple. The fine deposit is in the clays of the Allison member of
the Chacra sandstone. Seemingly, this fine exposure was used extensively
by the early inhabitants of the canyon. A small gully is now
cutting into the area of the richest deposits. This was probably begun
by the mining operations of long ago.