S-1: The object is called a ventifact or dreikanter or wind-cut stone. The surface is frosted. Look along one of the edges and find the spot where someone has broken it and see the high luster of the unfrosted quartz. The flat surfaces of the pebble resulted from the erosion of wind hence its name. The sample came from a dune field on Long Island, New York.
S-2: This gastrolith has a polished surface. I collected it and a dozen others from the rib cage of a dinosaur. Dinosaurs and birds are thought to have swallowed stones and sand to aid in the grinding and digestion of their food. No one has ever seen a dinosaur do this, why? Are their other way this stone could have become polished; yep.
S-3: This cobble from a stream in the Colorado Rockies has some of the finest percussion marks that you will ever see. Certainly these formed by on cobble smacking another in a high velocity stream. I should know I crossed the stream, just barely and got bruised feet in the process.
S-4: This cobble from a North Carolina Native America site has real faint percussion marks, you really have to look for them. Their faintness is probably due to the Native Americans using it to grind grain. Now are the percussion marks due to cobbles basing against one another in a stream or did someone get made and bash something with it?
S-5: This boulder has one flat surface, which has a few percussion marks. The chunk of rock is known as a core. It was found on top of a lava flow near Prescott, Arizona. Native American first ground down the flat surface to prepare a platform from which they later struck flakes for the manufacture of projectile points, scrapers, etc. The percussion marks resulted from bashing the platform to knock loose a flake. (Real pretty interpretation don’t you think?)
S-6: This polished pebble was collected from some very fresh un-weathered glacial till of Pleistocene age, dinosaurs were long dead at this point and it is to big for a bird to have used. So lets interpret it as glacial polish.
S-7, S-8, S-9, & S-10: Cobbles with striations. These were all collected from Pleistocene diluvium (glacial tills) in Iowa. S-7 was picked up from a groove, which it was in the process of carving in the limestone bedrock just north of Iowa City, Iowa. A valid interpretation is that all of these striations are due to glacial action. But do not forget the Appalachian State Prof. who got laughed at when someone pointed out that a logging chain had made the striations, which he had used a proof that the Blue Ridge of North Carolina had been glaciated!
S-11: A cobble from the shore of Lake Superior near Calumet Minn. The protolith of this cobble is a conglomerate. Note how the differences in the weathering resistance of each of the grains of this cobble have resulted in a very ruff surface that illustrates quite well differential weathering.
S-12: Two more fine examples of differential weathering.
S-13: This pebble has a polished surface but some folks would not even classify this as a sedimentary pebble. It comes from a diatreme where deep seated gasses explosively erupted through the sedimentary pile ripping loose a chunk of Devonian shale and abrasively polishing it in a matter of a few seconds while it traveled upwards in the explosive pipe. (I like to write pretty geopoetry.)
S-14: The surface of this coke bottle is frosted, but not by the action of wind but by rolling around in the surf at Carolina Beach, NC. Litterbugs do serve a purpose.
S-15: This is a piece of black granite (yep it be granite) from Cold Spring, Minn. This is the same stone used in the Viet Nam Memorial. At the quarry they cut it and then use silicon carbide abrasives on it to give it a polished surface (I watched it happen therefore this is a correct interpretation). Some less than scrupulous people do the same thing to pebbles to produce dinosaur gastroliths that they then sell to unsuspecting tourist for exorbitant prices. Nice rocks for the coffee table; an incorrect, but for a tourist, a valid interpretation of their origin!!!
S-16: A cobble from the Lance Formation of the Big Horn Basin of Wyoming with very obvious impression marks. This was collected when I was at geology field camp as an undergraduate. It comes from the apex of a tight fold that was cropping out along the highway in one of the area, which we had to make a geologic map of.
Remember the above bold type terms are descriptive terms, they have multiple possible interpretations as to their mode of formation.