Eleven obsidian projectile points (4%) were made from Ob2 obsidian; a surprisingly high number under the operating assumption that fracture and visual quality of the material were important characteristics in bifacial tool production. Briefly exploring these eleven Ob2 projectile points may shed light on the characteristics that guided material selection in prehistory.

Ob2 materials form a much higher percentage (15%) of the obsidian flake surface collection than do Ob2 bifacial tools (4%) of the obsidian tool collection, which suggests that Ob2 material was being knapped but apparently not bifacially retouched.

The projectile points made from Ob2 material tend to have small or low-density heterogeneities that do not appear to greatly affect knapping quality, although visually the pieces appear mottled. These points were found in the south-eastern part of the study area in the San Bartolomé area (including one from a Late Formative excavated context), and in the reconnaissance blocks 4 and 5.

Table 6-9. Projectile Points made from obsidian containing heterogeneities (Ob2).

Table 6-10. Ratio of Obsidian Projectile Points with heterogeneities.

Due to low cell counts, conducting a chi-squared test required aggregating the counts from the Middle and Late Archaic Periods. A chi-squared test on the aggregated table (Table 6-10) showed that the difference between projectile points from Group 1: Middle and Late Archaicand Group 2: the Terminal Archaic through the Late Horizonwith respect to the use of obsidian with heterogeneities is very significant (c²= 9.976, .005 > p> .001). It appears that Ob2 was very significantly less used for point production in the later time period.

Note that the material used for projectile point production in Block 2 was at times the cloudy Ob2, and it is likely that this reflects, in part, the availability of this material on the southern and eastern flanks of Cerro Hornillo. However, the vast majority of the Ob2 obsidian flakes are actually found in Block 3, at the site of Taukamayo.