It's great to receive all the comments. First to address:
Why not experiment to find out if we have any good rocks for teapot clay dust in any other location?
I may go that route, but what I'm also attempting to confirm here is the uniqueness of purple clay's properties. There are a thousand varieties of clay, and some will do as replacements in the right situation, however, if Yixing were replaceable or replicable in the lab, then the value and praise of this clay as optimal for certain teas, would be somewhat unfounded. Some assert that Yixing purple clay has no other alternative which is as satisfying for tea. For my purposes, rather than tea, it's a product design venture for which the same properties that make Yixing purple clay ideal in the tea realm give it value in my intended application: the joint, often opposed properties of stoneware strength and earthenware porosity. In the world of ceramics, we do not find these two characteristics in the same natural clay body quite so effectively joined elsewhere, to my knowledge. (I am not a professional ceramacist, but have picked up a good deal of info in that area over the past few years of research).
To quote Liang:
"Clays similar to Yixing clay in colour and general appearance can be found in many parts of China and in Europe too, but they lack the sandy consistency that makes Yixing clay unique."
The sandy texture is valuable in my application, and related to other aspects of Yixing purple clay's material properties. In more detail, and related to the point on other clays in a vast world:
"[...] this clay differs from materials used in the making of other wares in China, Japan or Europe, which make look similar to zisha ware [purple clay ware] but are in fact made from different materials with different qualities. [...] Zisha clay is of the kaolin-quartz-mica type, with a high content of iron oxide. This high iron content distinguishes zisha clay from other materials of kaolin type, giving the ware its dark purplish-red color. Kaolin also gives zisha ware its good fired strength and stone-like quality, and the presence of mica in the clay body probably accounts for its rough, sandy texture. Zisha ware is fired to 1100-1200 degrees c. [...] At such high temperature most red earthenware would vitrify – that is, become hard, causing the formation of glass in the clay body and a loss of porosity. Because of the high kaolin content of zisha clay, however, when the zisha ware is fired to a temperature of 1200 degrees c it still retains a certain degree (about 2%) of porosity [...] and may be connected with the structure of the large quantity of aggregates found in zisha ware, a high proportion of which are formed from the mineral group kaolinite. Two types of pores are formed inside the clay body; the 'closed' type (in the inner structure of the aggregates) and the 'open type' (around the periphery of the particles of aggregates). When the ware is fired, these aggregates shrink and form around themselves a continuous layer of pores which give zisha clay its unique and valuable 'breathing' quality – the attribute which makes it especially suitable for making of teapots and flower pots."
At this stage, its seems zisha is indeed unique, but that may be overturned with further research and experimentation in the lab and studio. The first step is to obtain the material!