Chert volcanic origin

The majority of cherts from the inland site of Fiais were also from calcareous deposits. Figure 4 shows that Al and Ti increase at the interior site, which is buried in a clay-rich soil. It is admittedly difficult to determine whether the increases in such elemental concentrations are caused by di-agenetic factors or by inhomogeneity of the materials. These changes stand out in sharp contrast to the majority of cherts from Samouqueira, which on the basis of thin-section analyses, are of a meta-volcanic origin. These cherts are less susceptible to weathering and appear to have experienced little... 

In the Chichibu Zone, the intimate association of abundant strata-bound Mn-Fe deposits, limestone-dolomite and silica (chert) with basic volcanic rocks suggests an ocean-ridge hydrothermal origin. 

In Chapter 2, Hancock, Pavlish, and Sheppard give an example of a case in which visual examination of stone tools was not adequate to differentiate between lithic artifacts that were produced from rocks that were very different in their origins. During the Mesolithic and early Neolithic times, the inhabitants of what is now Portugal used a variety of materials. Although most of the stone tools were classified by the archaeologists as sedimentary cherts, Hancock concluded that many tools were made of volcanic rhyolite. 

The Fairweather Formation is younger than the Duncan Formation and was originally described by McCjregor (1965b) as a crushed quartz-sandstone. Stump et al. (1976) classified it as a massive, silicic, porphyritic volcanic rock including nonporphyritic varieties and volcanic breccias. In addition, the Fairweather Formation contains thin beds of marble and chert. Wade and Cathey (1986) considered that the lithologic composition of the Fairweather Formation resembles the Taylor Formation in the Shackleton Glacier area and therefore correlated the two formations as indicated in Table 6.1. 

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