3.6. Obsidian Use in the South-Central Andes

Obsidian was knapped into relatively few artifact forms in the south-central Andes. The most common formal stone implement was a bifacially flaked projectile point, but other bifacial tools such as knives and scrapers were also commonly produced throughout the consumption region. The other major technical class for obsidian artifacts were simple flakes. As a sharp, but fragile, cutting implement, a freshly struck obsidian flake was potentially useful for butchery and wool shearing purposes. Dransart (2002: 108-109) reports that in rural communities modern wool shearing is accomplished either with the lid of a tin can that has been folded over so as not to cut the user's hand, or with a broken piece of bottle glass. Contemporary herders in the Colca region report that obsidian flakes, and sometimes broken glass vessels, are used for castrating animals because it was explained that as non-metal tools do not oxidize, they are less likely to introduce infection into the animal (T. Valdevia 2003, pers. comm.).

A distinctive Andean method of camelid slaughter can be accomplished with a small, sharp flake is described by George Miller (1979: 27-36). The ch'illamethod of slaughter consists of laying the animal down, cutting a small incision near the sternum with a small flake of stone, and reaching in and manually breaking the ascending aorta where it leaves the heart. Ethnoarchaeological studies have shown that simple flakes are often used in butchering and shearing, and therefore a prehistoric association between pastoral facilities and lithic flakes, both utilized and unutilized, seems probable.

3.6.1. Variability in Andean obsidian use

In many regions of the world prehistoric artifacts made from obsidian can be generally classified by whether the principal function is for display or for some utility more directly related to subsistence. In Mesoamerica and the ancient Near East, both areas with complex societies and elaborate stone tool production, obsidian was used to make bowls, vases, eccentrics, seal stamps, statuettes, and tables, as well as items of personal decoration such as labrets, ear spools, necklaces, and pendants (Burger, et al. 1994: 246). Craftspeople also developed efficient, high utility obsidian technologies as well, such as prismatic blades, a form that allows archaeologists to quantify cutting edge to edge-length, error rates, and other efficiency measures.

In the south-central Andes the diversity of artifact forms made from obsidian is relatively low, and it is difficult to differentiate display from utilitarian applications. For example, obsidian projectile points are both sharp and highly visible, suggesting that the points had a display function that underscored their utility as a weapon and as a cutting tool.

Hafting in the Andes

Archaeological evidence shows that bifacially flaked obsidian implements were hafted in a variety of ways. The majority of the hafting evidence from the Andes comes from coastal sites due to superior preservation. Projectile points were hafted to spears, spear thrower darts, and arrow shafts. Obsidian bifacial tools were also hafted to wood or bone handles for use as knives. Hafting materials varied regionally, but hafting was often accomplished using gum or resin, and hafts supported with cotton string have been found in some coastal sites (Carmichael, et al. 1998: 79).

Evidence of use of obsidian

The artifact types predominantly manufactured from obsidian include projectile points and tools for cutting and shearing tasks. While simple flakes are wide-spread and were probably used abundantly for butchering, scraping, and shearing purposes, the utility of obsidian flakes is frequently discounted when flakes are relegated to the "debitage" or "debris" class. In Andean studies bifacially-flaked instruments are the most commonly analyzed obsidian artifact class in archaeological reports from sites in the Andes.

Obsidian artifacts are sometimes found in association with iconographic representations of dark colored artifacts that are similar in appearance to the very obsidian artifacts found in that context (Burger and Asaro 1977: 15). Such is the case with black-tipped darts and knives depicted on Ocucaje 8 through Nasca 6 ceramics and textiles, and obsidian artifacts found in tombs from those contexts. Building on the discussion in Burger and Asaro (1977: 13-18), examples of obsidian artifacts from the south-central Andes follow.



Application

Form

Provenience

Description

Reference

Weapon (probable dart point), conflict

Point

Looted tomb at Hacienda Mosojcancha, Huancavelica.

A point made from obsidian was found embedded deeply in a human lumbar. (Figure C-10).

(Ravines 1967)

Weapon, with spear throwers

Point

Grave 16 at Asia,
(central coast of Peru).

Preceramic context.

Found in association with spear throwers

(Engel 1963: 56;Uhle 1909)

Weapon, hafted

Point

Tombs at Hacienda Ocucaje, Epoch 10.
Early Horizon context.

Points hafted with gum and, in one case, cotton thread to wooden foreshafts.

(Burger and Asaro 1977: 14)

Weapon

Point

Carhua (south coast , Peru)

Point penetrating through arm muscle near humerus (Figure C-1).

(Engel 1966: 212)

Weapon,

dart

Point

Paracas Necropolis

Well-preserved harpoon (Figure C-9).

(Engel 1966: 180c)

Weapon,

dart

Hafted projectile

depiction

Nasca Phase B1 and B2 diagnostic attribute

Phase B has "Atlatl darts (arrows) in series as ornaments" (Figure C-6).

(Carmichael, et al. 1998: 151)

Weapon, poison

Point

Eastern Lake Titicaca

Obsidian is among point types dipped in strong poison from herbs, perhaps curare.

(Cobo 1990 [1653]: 216-217)

Weapon, bow and arrow

Point depiction

Tiwanaku pottery

Archers with bow and black

tipped arrows depicted on a Tiwanaku q'ero(Figure C-4).

(Bennett 1934: 426-459;Posnansky 1957: plate XXa)

Weapon, hunting

Point depiction

Nasca B vessel

Depiction of darts sailing towards a group of camelids .

(Burger and Asaro 1977: 16)

Tool, Ritual

Knife depiction

Nasca B pottery

Black knives associated with taking of trophy heads.

(Burger and Asaro 1977: 15)

Tool, Ritual

Knife depiction

Nasca textiles, Epoch 1

of EIP

Black knives associated with taking of trophy heads.

(D'Harcourt 1962: 110, 112)

Tool, Ritual

Knife, hafted

Early Nasca

Bifacial knife hafted to painted dolphin palate (Figure C-5).

(Disselhoff 1972: 277)

Decorative, Ritual

Mirror fragment

Huancayo, Middle

Horizon 2 context

Fragment of obsidian mirror ground and polished to .4 cm thickness.

(Browman 1970: 86)

Decorative, Ritual

Mirror

Huarmey, Wari

Mirror mounded in carved wooden hand (Figure C-8).

(Lavalle and Perú 1990: 185)

Medical

Obsidian knives with blood-stains.

Cerro Colorado, Paracas

Part of medical kit that also contained a chachalote (sperm whale) tooth knife, bandages, balls of cotton, and thread.

(Tello 1929: 55)

Medical

Chillisaa kala, Aymara for "black flint"

Titicaca Basin

Speculation about tools used for trephination.

(Bandelier 1904;Marino and Gonzales-Portillo 2000)

Table 3-10. Examples of obsidian use in the south-centralAndes (part 1).



Application

Form

Provenience

Description

Reference

Medical,
Ritual

Material used in folk cures

Canchis, Cuzco; and elsewhere

Modern use in folk cures, the stone was believed to have curative powers.

(Burger and Asaro 1977: 17;Cobo 1990 [1653])

Medical,
Ritual

"knives of crystalline stone"

Titicaca Basin ( ?)

Abdominal surgery by "sorcerers"

(Cobo 1990 [1653])

Animal castration

Flakes, unmodified or retouched

Colca

"We use sharp pieces of obsidian or glass to castrate herd animals it doesn't cause infection like rusted metal knives."

T. Valdevia 2003, Pers. Comm. (my translation).

Shearing

Flakes, unmodified or retouched

Andes

"Aboriginal shearing required special implements, perhaps obsidian knives." Some modern pastoralists use broken glass and tin lids for shearing.

(Dransart 2002: 108-109;Gilmore 1950: 446)

Table 3-11. Examples of obsidian use in the south-centralAndes (part 2).

Many of these examples are shown in Appendix C. of this volume. While the diversity of artifact forms was relatively low, it is evident that the visual and fracture properties of obsidian were relevant to the tools that were used from this material. Further north in the Andes, in Ecuador, a greater percentage of obsidian artifacts seems to have filled a primarily decorative role, including abead, an ear spool, and three polished mirrors(Burger, et al. 1994: 246).

The evidence of use lithics may also take the form of cutting and scraping marks on faunal remains, but the lithic material type can rarely be established by these means. The continued use of glass and obsidian in modern contexts for shearing, butchery, and castration suggests that the prehispanic metals such as copper and bronze did not displace obsidian and other lithic materials for utilitarian tasks. Prehispanic metals were used largely for display, although metals were used in some weaponry, such as mace-heads (Lechtman 1984).

Obsidian in warfare

The evidence for obsidian use in conflict in the Andes comes from a variety of archaeological and ethnohistorical sources, but it is primarily in the form of indirect evidence. The data reveal a great expansion in the production of small obsidian projectile points after the onset of a food producing economy. The majority of Late Horizon weapons that the Spanish faced during their invasion appear to have been bola stones and percussion weapons like maces and slings(Cahlander, et al. 1980;Korfmann 1973), as well as padded armor.

Archaeologists working in the south-central Andes vary historically in their assessment of the use of projectiles in the highland region(Giesso 2000: 43). Bennett(1946: 23)asserts that the use of bow and arrow were not important on the altiplano, Metraux(1946: 244-245)says that spear throwers were in use, while Kidder(1956: 138)indicates that evidence from projectiles show that arrows were widely used at Tiwanaku. Of the projectile points analyzed by Giesso from Tiwanaku, 19% were made from obsidian, with the highest concentration of points coming from excavations in the civic/ceremonial core at the Akapana East, K'karaña, and Mollo Kontu mounds(Giesso 2000: 228-238).

In a dramatic example of obsidian use as a weapon, one archaeological findError! Reference source not found.shows a probable spear or dart point penetrated the victim's abdomen from the left anterior abdomen and lodged on the anterior side of the lumbar vertebra.

Evidence of use of the bow and arrow in warfare

One of the strongest patterns in obsidian distributions in the south-central Andes is the sudden onset of obsidian use with series 5 projectile points in the Terminal Archaic, after 3300 cal BCE In defining the small type 5D projectile points Klink and Aldenderfer(2005: 54)suggest that the widespread adoption of these point types may reflect the use of bow and arrow technology, as these points fallwithin the size range described by Shott (1997: Table 2) as associated with arrow points (although with substantial overlap with the size of the smaller dart points).

/misc/image011.jpg

Figure 3-14. Type 5d projectile points from a Terminal Archaic level at Asana and Early Formative levels at Qillqatani, from illustration in Klink and Aldenderfer (2005: 49).

Additional metrics for differentiating arrowheads from dart and spear points have been suggested by Thomas (1978: 470) and Patterson (1985). With Mesoamerican projectile points, Aoyama (2005: 297) has found a very significant correlation between evidence from microwear analysis and projectile dimensions in his effort to differentiate arrowheads from dart and spear points. The relationship between the mass of the item and the velocity and distance of the projectile are discussed in detail by Hughes (1998). She notes that the innovation of fletching allowed for balanced projectiles that had smaller projectile tips and lighter shaft materials, which in turn permitted greater distance and velocity in weapons systems (Hughes 1998). On a related point, the notched base in all type 5 projectile styles reflects a change in hafting technology. Greater impact loads can be absorbed by mounting projectiles tips with notched bases into slotted hafts (Hughes 1998: 367;Van Buren 1974).

Obsidian has a number of attributes that make it a particularly effective material for projectile point tips, most notably are the predictableconchoidal fracture qualities of obsidian that allow it to be pressure flaked into very small projectile points. The sharpness of freshly knapped obsidian margins is unrivalled, andethnographicallyobsidian is renowned as a brittle material that can fracture on impact, causing the fragments to produce greater bleeding in the victim of an obsidian projectile (Ellis 1997: 47-53). In materials science, obsidian has extremely low compression strength because it has no crystalline structure (Hughes 1998: 372). Due to the brittleness or lack of compression strength, missed shots can result in many broken obsidian projectile tips, and perhaps for this reason obsidian was not the predominant material for projectile point production until after the domestication of camelids when hunting was decreasingly the primary source of meat (as inferred from the ratio of camelid to deer bone in excavated assemblages).

Increased velocity and distance is possible with the use of bow and arrow, and obsidian has greater penetrating power, although lower durability, than other material types. Do these changes suggest a greater use of projectiles for warfare? Greater use of small, fletched projectiles might be expected in contexts where the individual needs (1) increased distance from the target (2) increased velocity, perhaps due to change in prey or to the use of padded armor. The use of obsidian may increase in contexts where one needs (1) a material that can be knapped into small, light projectiles as discussed above, (2) increased penetration with sharper material, (3) decreased concern for durability because in warfare the weapon will perhaps be retrieved by the opponent.

Although empirical evidence for warfare is scarce in the Terminal Archaic in the highlands, a study of 144 Chinchorro individuals from Terminal Archaic contexts in extreme northern Chile found that one third of the adults suffered from anterior cranial fractures that probably resulted from interpersonal violence, and men were three times more likely than women to have these wounds (Standen and Arriaza 2000). These wounds appear to have been caused by percussion weapons like slings, but the coastal evidence for interpersonal violence in this time period is strong. Additional support for the introduction of the bow and arrow in the Terminal Archaic come from the region among Chinchorro burials in coastal Northern Chile. Bows among the Chinchorro grave goods date to circa 3700 - 1100 cal. BCE, or the Terminal Archaic and Early Formative (Bittmann and Munizaga 1979;Rivera 1991;Standen 2003).

Possible use of poisons on projectile tips

A potential explanation of widespread adoption of the small type 5D projectile points is the greater availability of poisons that reduced the need for heavy, destructive projectiles.South American poison arrows are usually quite small and such arrows are frequently tipped only with a sharpened wooden point. According to Ellis(1997: 55),virtually all ethnographic examples of arrow use include some kind of poison applied to the arrow in order to have either a toxic or a septic effect on the victim. Ellis observes that due to the great variety of substances used to create such toxins, in many regions of study these substances would probably contaminate any chemical attempt to use residue analysis to differentiate the types of poisons used, or even the prey that was hunted, with a particular used projectile point.

A variety ofhighly effective poisons are applied to the tips of projectiles by hunters in the Amazon Basin today(Heath and Chiara 1977).In the prehispanic Andean highlands, trade contacts with the Amazonian lowlands to the east may have made available poison concoctionsfor application to projectiles, most notoriously the fast acting paralysis alkaloid curareprepared from the vine Chondrodendron tomentosum(Casarett, et al. 1996).

Bernabé Cobo (1990 [1653]: 216-217) discusses the use of bow and arrow with poisons by "expert marksmen" in his chapter on warfare. Hedescribes the widespread and expert use of the sling for warfare, which is consistent with reports elsewhere on the use of slings, but then he states that bow and arrow were more significant in warfare.

The most widespread weapon of all the Indies, not only in war but also in the hunt, was the bow and arrow. Their bows were made as tall and even taller than a man, and some of them were eight or ten palms long, of a certain black palm called chontawhose wood is very heavy and tough; the cord was made of animal tendons, cabuya, or some other strong material; the arrows, of a light material such as rushes, reeds, or cane, or other sticks just as light, with the tip and point of chontaor some other tough, barbed wood, bone, or animal tooth, obsidian point, or fish spine.
Many used poisoned arrows, their points anointed with a strong poison; but, among the nations of this realm, only the Chunchosused this poisonous herb on their arrows, and it was not a simple herb, but a mixture of various poisonous herbs and vermin; and it was so effective and deadly that anyone hit by one of those poisoned arrows who shed blood, even though it might be no more than the blood resulting from the prick of a needle, died raving and making frightful grimaces(Cobo 1990 [1653]: 216-217).

The Chunchos ethnic group is described as living in the "forests east of Lake Titicaca on the border of the Inca Empire".It is possible that Amazonian poisons became available in altiplano during the Terminal Archaic due to expanding exchange networks, together with Amazonian hallucinogenics and other lowland products, dramatically altering the efficacy of arrows. As a sharp but lightweight weapon, obsidian tipped arrows would have represented an effective poison delivery system to animal and human victims alike.

While there is no direct evidence for the use of Amazonian poisons on the altiplano, the dramatic change in projectile technology with the type 5D type, co-eval with expanding exchange networks in the region, suggest that a new technology for weapons systems, such as poisons and new shaft and fletching materials, may have influenced the design of projectiles in this time.The transitional economic context of the Terminal Archaic involved many changes, including shifts in both food production and interregional exchange, and the technology of lithic production show significant alterations that correspond to this period.

Multiethnic access to geological sources in the Andes

Salt procurement in the Amazon basin on the eastern flanks of the Andes provides an example of multiethnic access to a raw material source. During annual voyages to the Chanchamayo salt quarry ten days outside of their territory, the Asháninka of the Gran Pajonal (Ucayali, Peru) combine salt procurement with exchange with neighboring groups who share access to the source(Varese 2002: 33-35). Arturo Wertheman, a missionary who traveled through the region in 1876, explains

Throughout the year small bands of Asháninka traders traveled [the Gran Pajonal] paths to obtain salt, carrying with them tunics or ceramics to exchange for other items and for hospitality. With them traveled their traditions, their hopes, and the information of interest to their society. The Pajonal, the vast center of Campa territory not yet invaded by whites, appears to have been the center of culture and tradition through which the Indians journeyed, like a constant flow of life through their very society(Varese 2002: 120)

Other ethnographic examples of multiethnic access to salt quarries are mentioned in the ethnographic literature. Oberem(1985 [1974]: 353-354)describes access by both the Quijo and the Canelo people to a large rock salt quarry located on the Huallaga River, a tributary to the Amazon lying further north on the border of Peru and Ecuador.

In the Cotahuasi valley of Arequipa, to the north of the Colca valley, the rock salt mine of Warwa [Huarhua] has been exploited since Archaic times(Jennings 2002: 217-218, 247-251, 564-566). Access to the Warwa quarry, which lies near the border of the departments of Arequipa, Ayacucho, and Apurímac, is described by Concha Contreras(1975: 74-76)as including caravan drivers from all three of those neighboring departments.

El primer viaje lo hacen, mayormente, en el mes de abril. En esta época cientos de pastores se concentran en esta mina. El camino es estrecho y accidentado hasta llegar a la misma bocamina…Desde el fondo de la mina los pastores cargan a la espalda la cantidad de sal que necesitan llevar, de tal manera que hacen muchos viajes al socavón de la mina. En todo este tramo tardan 4 días, porque después de la mina, siguen cargando en la espalda hasta una distancia de aproximadamente cinco kilómetros, donde quedaron las llamas pastando, puesto que hasta la misma mina no pueden entrar juntamente con sus llamas(Concha Contreras 1975: 74).

There appear to be a number of protocols associated with salt acquisition at Warwa. Notably, the multiethnic visits by caravanners from various departments coincide in April despite the tight working quarters at the salt mine. Furthermore, there seems to be concern for impacts in the much-visited the mine area itself. The cargo animals are actually grazing a distance from the quarry and humans are obliged to carry the loads to these areas instead of attempting to load the animals close to the mine. These cases of multiethnic raw material access provide examples of the social and institutional nature of access to unique geological sources, and the focalized attention that these source receive from surrounding ethnic groups. The analogy with regional acquisition and diffusive transport of the raw material is perhaps the closest modern analogy to the nature of prehispanic obsidian quarrying that remains in the Andes.

3.6.2. Symbolic significance of obsidian

Inferring the symbolic significance of obsidian in the prehispanic Andes involves approaching the topic from a several lines of evidence because there are few direct indicators of valuation and symbolic meaning of obsidian in the Andes. Below, these issues are raised as a series of questions that may, or may not, be answered with archaeological evidence from the region:

(1) How did the symbolic importance of obsidian change through prehistory?

(2) Do changes in use of obsidian reflect local geographic availability?

(3) Did the visual properties of obsidian resonate with Andean aesthetic traditions?

(4) Was there social significance in the visible differences between major obsidian types?

Part of the difficulty in inferring the symbolic properties of obsidian is the result of a relative reduction in the importance of obsidian during the Late Horizon and Colonial period, to judge from ethnohistoric accounts. Ethnohistoric sources are a prime source of information, although through Spanish eyes, of cultural significance and symbolic value in the prehispanic Andean world. Despite the apparent decline of obsidian use in the late Prehispanic and Colonial periods, archaeological distributions suggest that obsidian had substantial cultural and ceremonial associations in particular contexts during in Prehispanic times.

How did the social and symbolic importance of obsidian change through time and space?

Obsidian flakes and bifacial tools were sometimes included as grave goods from the Terminal Archaic (3300 cal BCE) and onwards. Ethnohistoric accounts and archaeological evidence indicate that obsidian "knives" were employed in ritual practice as well as in medical procedures throughout the region, although it is not evident if these were bifacially-flaked tools or simply freshly struck flakes. In addition, concentrations of flakes of quartz as well as obsidian from a variety of non-local sources were found in the Tiwanaku ceremonial mound of Mollo Kontu in a regular pattern that was interpreted by Couture (2003) to indicate deliberate inclusion in clay fill rather than accidental redeposition.

Based on analogy from other goods, it is possible that in areas where obsidian is used in ceremonial contexts a finely-made obsidian implement may have been less likely to have been exchanged as an alienable product traded in barter. In some historical contexts, a ritual item may become a singular item and acquire a distinctive 'genealogy' related to its social history that precludes it from being bartered and circulated in equivalence for something ordinary such as a sack of potatoes (Hodder 1982;Kopytoff 1986).

However, on the whole, obsidian appears to be one of a number of products that escapes easy classification. On one hand, obsidian circulated in established networks controlled by llama caravan drivers who were responsible for the distribution of a variety of goods on the altiplano. These caravans appear to have been organized by households and derived communities of relatively humble means, to judge from other aspects of their material lives excavated at sites like Qillqatani. On the other hand, as a luminescent material with irregular spatial availability, obsidian had properties that qualify it as a "prestige good" in many contexts (Hayden 1998). In terms of rituals organized and performed on a local level, obsidian was probably one of a number of materials that were traditional but non-the-less slightly rare like ochre and shell. Craig (2005: 683-693) explores the evidence for the symbolic importance of discrete color groups in ritual items like ochre and obsidian in the Titicaca Basin Archaic and Formative site of Jiskairumoko by examining the patterning of obsidian and ochre in comparison to what were common-place, functional applications of these goods.

From the perspective of early aggrandizers in the Terminal Archaic and Formative Lake Titicaca Basin, obsidian probably represented a somewhat elusive product for labor investment and therefore was not a principal substance used in elite strategies by the time of the Middle and Late Formative. From the perspective of prestige technologies serving the agenda of aggrandizers by locking up surplus labor (Hayden 1998), the issue might be considered in terms of the following factors:

(1) Obsidian was relatively easy to acquire, perhaps too easily acquired, for the people living in the highlands of Arequipa; and it was not concentrated in specific, controllable points accessed only through mine shafts.

(2) Obsidian has functional properties that assured its continued circulation for the production of cutting and piercing implements, making it insufficiently rare to have served as a "preciosity" (Clark and Blake 1994;Goldstein 2000).

(3) While craft specialization was fostered in more closely-controllable contexts in regional centers during the Formative, obsidian sources were perhaps sufficiently distant to have escaped this kind of specialized craft production. In contrast, consider the various non-utilitarian obsidian products made by craftspeople in Mesoamerica, discussed above.

(4) As obsidian was primarily made into projectile point tips, it was perhaps associated with hunting, or the threat of violence. In some regional traditions, such as in Nasca iconography, obsidian appears to have been associated with trophy head taking. However, in the south-central Andean highlands there is no evidence of a direct association between violence, emerging leadership, and control of surpluses along the lines of Hayden's (1995) despotic leader model.

Obsidian products, particularly finely-made bifacial tools, were perhaps one of a series of items that served to differentiate status-seeking individuals in early transegalitarian contexts, but with later crafts investment obsidian appears to have been assigned a relatively specific role for projectile point production and for cutting implements.

Do changes in use of obsidian reflect local geographic availability?

One way to examine the social and symbolic significance of obsidian is to examine the changing use of the material as availability declines with distance from the geological source. To judge from the distant consumption zone, obsidian was used in both mundane contexts and also in ritual or ceremonial contexts. At Tiwanaku, obsidian was found dispersed into the fill of ceremonial mounds (Couture 2003). It is also sometimes found in Titicaca Basin burials as of the Terminal Archaic. As reported by Craig (2005: 570-574, 679-682), at Jiskairumoko and at other sites in the Ilave valley, obsidian has been found in burials dating to 3300 cal BCE and later along with other non-local goods including lapis lazuli (sodalite) beads, gold discs, and gold beads, as well as ritual items like a camelid effigy made from bone. If the associations of obsidian with ritual power were related to its non-local origins, one might expect this pattern to have been weaker in closer proximity to the Chivay source. Items from ritual contexts, such as grave goods from the Colca Valley, and in close proximity to the Chivay obsidian source, may provide data to test this hypothesis.

Do the unusual visual qualities of obsidian resonate with Andean traditions?

Andean traditions place a priority on visual attributes, and links between the visual purity of a material and its essence have been widely noted in some segments of the Andean literature. As a natural glass, the aqueous properties of obsidian cause the material to reflect light which may display the workmanship of obsidian artifacts, as well as the potential sharpness of obsidian tools. Obsidian used for prehistoric tool production was often a homogeneous glass that was visibly consistent, pure in color, and sometimes transparent or banded. The importance of visual qualities of metals in the Andes has received greater attention:

The social arena in which metallurgy received its greatest stimulus in the Andes was the arena dominated by status and political display. An underlying cultural value system that appears to have strongly influenced the visual manifestation of status and power was a color symbolism oriented around the colors of silver and of gold. The most innovative and interesting aspects of Andean metallurgy arose from attempts by Andean metalsmiths to produce metallic gold and metallic silver surfaces on metal objects that were made of neither metal (Lechtman 1984: 15).

In Andean metallurgy, the appearance of consistency in color, reflectivity and material was prioritized because visual characteristics conveyed information about the inherent essence and animation of the object (Lechtman 1984: 33-36).

There is little direct support in Andean archaeological or ethnohistorical sources for inference regarding how obsidian was perceived, but it would be consistent for obsidian, a stone with the appearance of watery luster, to be associated with ceremonial power and ritual sacrifice given the well-demonstrated importance of stone and water in Andean cosmology.

Were the visual differences between obsidian types in the Andes important?

Visible differences between obsidian chemical types in the region are principally in terms of nodule size, fracture characteristics, glass color, and cortex. While nodule size and fracture characteristics are believed to have been important determining factors in explaining which obsidian types were circulated widely in prehistory (Burger, et al. 2000: 348), glass color is more of visual aesthetic issue. The obsidian sources in the south-central Andes are predominantly black or grey. Obsidian from the Chivay source is often a transparent grey and banded, and Quispisisa obsidian sometimes has a red coloration, although Burger et al. (2000: 314) state that the Quispisisa type is visually indistinguishable from Alca obsidian. As with many goods with discrete places of origin, these visual differences communicate information about the spatial origin of the stone that would have visually linked the material with regions and socio-political groups to knowledgeable viewers. To Brooks (1998: 452;1997) the transparency of Chivay obsidian was a reason for its wide circulation in prehistory. Others have commented on the transparency of the material including Giesso (2000;2003), and Burger et al (2000: 296). Giesso (2003: 368) observes that archaeological and ethnographic evidence from the Andes indicate that "transparent elements were viewed as mediators between different cosmological worlds". Further study may permit evaluation of observed patterns in the contexts of obsidian use that are linked to color.

Discussion

The social and ritual significance of obsidian in particular prehispanic Andean contexts appears to have varied across time and space, and with further research in the region into evidence of production and consumption these differences will be better understood. Archaeologists have established that the visual attributes of particular materials like metal were important in the late Prehispanic Andes. If this mode of interpretation may be extended, high quality obsidian shares some visual characteristics with metal such as shininess and an appearance of material purity. Furthermore, obsidian from particular areas was often visually distinct and this may have conveyed information in regions such as Moquegua where a variety of obsidian types have been encountered. Obsidian was irregularly available across the landscape, and the mere possession of this highly visible material in obsidian-poor regions had possible social significance because it suggested that the holder participated in long distance exchange networks or had alliances with groups in obsidian-rich areas.