Burley clay. Note the oolitic structure, the “burls.” From a diaspore pit near Swiss.
Burley clay is a fire clay intermediate in alumina content between flint clay and first quality diaspore. It takes its name from the oolites (rounded pellets of diaspore) which are scattered through a flint clay base and which were called “burls” by the early clay miners. As the relative number of diaspore oolites increase, an otherwise flint clay becomes burley-flint, then typical burley, and finally grades into second quality and first quality diaspore. Clay in any stage of the variation may be found in some part of the diaspore region or pits. Most of the remarks written on diaspore apply as well to burley clay.
Sandstone
Sandstone is a rock made of sand-size particles more or less well cemented. It is recognized by the grains of sand which are dislodged or scratched loose when the rock is broken, or when scraped with a piece of steel or another hard rock. The old-fashioned grindstone is a sandstone nicely cemented by nature.
Sandstone bluff near mine entrance, Crystal City. (Photo courtesy of Pittsburgh Plate Glass Company.)
Sandstone occurs in thin layers to thick massive beds and deposits which may exceed fifty feet in thickness. In addition to possessing horizontal bedding and parallel bedding planes, some sandstone displays beautiful, intricate cross-bedding or cross-lamination.
The grains of sand composing the stone may be either angular or rounded. They may sparkle in the light from reflections from their crystal faces, or they may have dull, frosted surfaces. Sandstones are ordinarily nearly white in color except where the grains are covered with coatings of yellow or red iron oxide (rust).
