A research article on the clays added to terra preta
Very detailed
You need to be a geologist and chemist to read it but very good.
It seems other rocks apart from pottery may have been added to the soil as well? (I am having trouble getting my head arround article-translated form Portugese!) What is cauixi and cariapé?
http://www.scielo.br/scielo.php?pid=...pt=sci_arttext
Quote:
most of mineral grains were taken from fresh crystalline rocks and intentionally crushed and introduced into clay material as well as cauixi and cariapé.
The above described minerals and organic substances led to identify the following materials as raw materials for the ceramics:
1) clay material derived from weathering (saprolite/mottling zone) of fine crystalline and less frequent sedimentary rocks (indicated by clay-derived minerals and iron oxy-hydroxides, anatase and quartz );
2) fresh crystalline rocks crushed (feldspars, quartz and rock fragments);
3) organic materials (cauixi and burned cariapé).
The abundance of fresh feldspars, rocks fragments and roundless quartz indicate that coarse igneous rocks, e.g. granites, granodiorites, and even rhyolites and quartz of veins were used as temper, after crushing. It's possible that pre-historic Indians extracted the fresh rocks from the same place where they took the clayey saprolite.
To improve the plasticity of the raw material they introduce organic material like cauixi and cariapé, crushed quartz, or even old ceramic (waste) crushed, in an old process of recycling.
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