Monday, February 11, 2008
Doves in the Clay Pit
A pair of Turtle Doves sun themselves in the new clay pit whose first purpose is to remove the earth that is caving in my studio/garage wall. Click on the image for a closer view.
A hand formed piece made with my backyard clay has mica specs that reflect light - looks like glitter in the clay. Taos pueblo has this in their clay too, and you can see the mountain their clay has come from. I have been reading up in Michael Cardew’s Pioneer Pottery trying to get a better picture about clay. One thing in his discussion is about feldspar altering into kaolin, well with a couple of significant by products, anyway. What Cardew doesn't mention is that 80% of the earths rock is felspathic by definition, which just from the normal process of "kaolinization" might create a wide variety of possible or theoretical primary clays. Naturally that also creates many secondary clays. But possibly as different feldspars become more or less the same kaolin, these many rocks become clay, and clay may be more similar to other clays than the different rocks the come from. Page 24 has the usual system of classification of hydrated sheet structure minerals; the same system is followed in my Field Guide to Rocks and Mineral by Frederick H. Pough, though in greater detail. Cardew states that "granites" produce white feldspars and the whitest kaolins, diorite a pinkish or red kaolin, then discusses bauxitization and the process leading to high alumina fire clays. Moving on to "secondary clays" he mentions clays derived chiefly from micas, and suggests that biotite mica is the source of much of the worlds red clay. The origin of ball clay is skipped over, there is not much discussion of how under clays are derived, but it is the same in England as it is in Kentucky. There is coal over it, so tropical forests grew in the clay, extracting many of the minerals, regardless of whether the clay is kaolinite or illite in origin: once the minerals are stripped away it becomes a ball clay. Clays of volcanic origin are discuused: aeolian clays/montmorillonite (bentonite). No mention of primary clays/micas which are weathered or hydrothermally altered extrusives, e.g. lavas. Hank Murrow and David Stannard were able to shed light on this mystery. Cardew has discussion here of slip clays, marls, or ochres either but maybe elsewhere in the book. Ryoji Koie in his travels always attempts to find local clays of this type. One of the things that has me stumped right now is that the light-orange colored mudstones of Georgetown are compressed mica of which type seems to be the source of clays with same minerals, & what I am looking at here in Alexandria is weathering of this same mineral, ranging from mica sand all the way to a fine plastic clay. Unless I am missing some important point here. This region is mostly metmorphic rock and one of those metamorphic rocks is clay and mica schist. This rock is a possible origin of these clays. Maybe(?)
The hill is called "Strawberry Hill" in the 1946 plat. So "Strawberry Hill Gold" could be a nice descriptive name. The usual classification system:
kaolins fireclays ball clays stoneware clays earthenware clays slip clays
- ought to be applied for further description. My guess is that it will max out in the stoneware or earthenware range.