This petro-fabric was identified and described by Torvinen (2018) using the modified Whitbread (C:F:V) approach (Quinn 2013). Chemical analysis of thin sections selected from this petro-fabric were similar in composition to raw material samples collected from clay deposits in the Malpaso Valley of Zacatecas, Mexico. The raw chemical data were acquired using the Electron Probe Microanalyzer-Wavelength Dispersive Spectroscopy (EPMA-WDS) technique. Synthesized data for this petro-fabric are available at: https://core.tdar.org/dataset/458202/torvinen-2018-epma-wds-raw-data-for-sherd-samples.

This fabric class is characterized by coarse to fine glass shards in a typically brown to dark brown (PPL) glassy matrix that is often very dark brown in XPL with weak optical activity but can also be yellowish-white with slight to moderate optical activity (Figure B.7). Voids are commonly meso- and macro-vughs with rare mega-vughs or megaelongate voids that may be cracks and cause some sherds to be very porous. The clear visibility and intact nature of the glass shard inclusions suggest either little to no transportation from their parent material prior to clay formation or the intentional grinding of a welded tuff for use as added temper. Many of the glass shards exhibit varying states of devitrification (e.g., PP 200, 203; Figure B.8). Variation in the size (coarse to very fine) and density (very close to single spacing) of glass shards may be capturing a technological gradient. Additional data collection involving point counting and modal analysis are necessary to fully define the two potential sub-fabrics listed below.

1. Coarse Volanic Glass: Predominant temper is coarse (<1.2 mm) glass shards that has been added in moderate, low, or rare amounts.


2. Fine Volcanic Glass: Predominant temper is fine (<0.55 mm) glass shards that occur in low to rare amounts or are very densely packed (Figure B.9).