Q.Is this clay 100% Pyrophyllite Clay
A. All clay deposits will have a mixture of both minerals and potential types of clay due to the nature of the lava and the type of rock source that was melted or ashed in a given location during the early formation of the clay deposit. Imagine a lava soup with mixtures of various colors of mineral rock floating in swirls, streams and ponds prior to solidification or ejection from the volcano as lava ash.
From one cubic foot to another, mineral composition will vary, which in turn determines the clay variations by name. A large deposit of a similar type of clay will commonly be of a predominant mineral composition with minor variations found from one cubic yard to another, and then a possible streak of a similar but variable texture of the same clay or a different clay composition.
When unearthed and dug for transport to a clay mill site, small streaks or pockets of a mineral variation found in the ground that get into a truck load of the predominant clay are milled with the whole run and blended during the milling process.
Nature is not an exact science when it comes to earthen compositions. These variations exist in all clay deposits. So an average sample is taken to determine its composition, or several spot analyses are averaged to come up with an average composition.
The geologist that analyzed this deposit originally noted that on average, the clay composition was 85% pyrophyllite with a few other variations found mixed in naturally. Some areas will be 100% pyrophyllite, while other areas will have variations, yet there is no way to guarantee 100% pyrophyllite 100% of the time. It has to do with the size of an excavator and the impossible task of dodging all streaks and pockets not seen below the surface as a 4 foot hole is scooped out.
If someone is guaranteeing 100% pyrophyllite 100% of the time, they are either naive as to the actual excavation process and the ways of Nature, or they are just trying to sell something by being less precise.