These petro-fabrics comprise non-calcareous clays derived from the erosion of shale deposits (usually Eocene in date). They have a “clayey” appearance and can have intact pieces of shale or be completely disintegrated into a pure clay. They are often categorized macroscopically as "marl clay" fabrics, but the dominance of iron over calcareous material suggests shale clay is more appropriate. As such, their use for Egyptian pottery was likely prevalent although it is unclear which specific forms were made, and in which specific periods. One clear case is the shale clays exploited for pottery in the oases, especially the Kharga Oasis in the Neolithic and Predynastic period, and also in Roman times (for example, at Ameidha). ...
Intact shale fragments are characterized by a planar orientation, and can have voids surrounding them (i.e., ring voids) and interior planar cracks (see Whitbread, argillaceous rock fragments). The color and opacity of shale fragments will vary in thin section. Typically, medium to coarse in size, subrounded to rounded. Can have opaque granules.
At lower firing temperatures, the paste can be optically active in one direction due to the linearity of clay minerals related to shale (if wheel thrown).
Sand can be added and is identified by medium to coarse-sized, mostly rounded inclusions of quartz, with lesser potassium feldspar and polycrystalline quartz, and rare other sand-sized minerals or rock fragments.
Calcareous material can be present, ranging from rare to common. Finely dispersed calcareous material could be natural to the clay deposit, as shale and calcareous formations are often in association. In other cases, the calcareous material appears added due to its high amount and range of sizes.
Petrographic analysis of “Marl C” suggests this fabric should be considered as shale derived clay with natural, finely dispersed calcareous material. Intact shale fragments (argillaceous rock fragments) that have not fully become clay are typical. “Marl C1” is characterized by the addition of limestone/chalk (fine to coarse in size, subrounded to rounded). “Marl C2” is characterized by the addition of limestone/chalk and dominantly quartz sand, the latter medium to coarse in size and subrounded to rounded in shape. Some Marl C can have dark oblong clayey inclusions that are likely fossiliferous shale, in which the foraminifera have burnt out during the firing. Scum surfaces (aluminium calcium silicate) can be present relating to the movement of calcium salts to the vessel surface during drying and subsequent firing.
These petro-fabrics comprise non-calcareous clays derived from the erosion of shale deposits (usually Eocene in date). They have a “clayey” appearance and can have intact pieces of shale or be completely disintegrated into a pure clay. They are often categorized macroscopically as "marl clay" fabrics, but the dominance of iron over calcareous material suggests shale clay is more appropriate. As such, their use for Egyptian pottery was likely prevalent although it is unclear whi...
This description was compiled during the LCP Egyptian Ceramic Petrography workshop at IFAO in September 2017.
