Prismatic blade
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In archaeology, a prismatic blade is a long, narrow, specialized stone flake tool with a sharp edge, like a small razor blade.[1] Blade segments were sometimes distributed and exchanged, rather than a complete blade. This includes proximal, medial, and distal blade segments. The ratios of these segments can be used to determine whether tools were exchanged as complete blades or just fragments.[2] Prismatic blades are flaked from stone cores through pressure flaking or direct percussion.[3] However, the steps of blade production could be different between regions and time periods in Mesoamerica. It’s important to mention that much of what we know about blade production comes from only a few sites that were studied.[2] This process results in a very standardized finished tool and waste assemblage. This waste consisted of flakes created when knappers made errors or material imperfections that had to be corrected during core reduction.[2] The most famous and most prevalent prismatic blade material is obsidian, as obsidian use was widespread in Mesoamerica, though chert, flint, and chalcedony blades are not uncommon. The term is generally restricted to Mesoamerican archaeology, although some examples are found in the Old World, for example in a Minoan grave in Crete.[4]
Prismatic blades were used for cutting and scraping, and have been reshaped into other tool types, such as projectile points and awls. Additionally, broken blade fragments could be reused and turned into retouched points/punches, notched blades, and scrapers produced from transverse core tabs or longitudinal core fragments.
Prismatic blades are often trapezoidal in cross section, but very close in appearance to an isosceles trapezoid. Triangular blades (in cross-section) are also common. The ventral surface of the prismatic blade is very smooth, sometimes bearing slight rippling reflecting the direction of applied force and a very small bulb of applied force (indicative of pressure reduction). Flake scars are absent on the ventral surface of these blades, though eraillure flakes are sometimes present on the bulb. The dorsal surface, on the other hand, exhibits scar ridges running parallel to the long axis of the blade. These facets are created by the previous removal of blades from the core. The proximal end contains the blade's striking platform and its bulb of applied force, while the distal end will consist of a snap break, a feather termination, or a stepped termination.