This puzzling sample is a naturally polished <a href="https://en.wikipedia.org/wiki/Quartz" class="extiw" title="w:Quartz">quartz</a> nodule, dimensioned from 2 to 3 inches (about 50 mm, give or take).  The surface porosity reflects the jointing of the underlying quartz crystals, generally less than 1 mm thick, that radiate from the inner core.
<p>This piece was naturally ground from a quartz infill of a <a href="https://en.wikipedia.org/wiki/Arthropod" class="extiw" title="w:Arthropod">arthropod burrow</a> (a <a href="https://en.wikipedia.org/wiki/Trace_fossil" class="extiw" title="w:Trace fossil">trace fossil</a>) common and peculiar to the <a href="https://en.wikipedia.org/wiki/Cottonwood_Limestone" class="extiw" title="w:Cottonwood Limestone">Cottonwood Limestone</a> ( see unpolished quartz nodule example in the <a href="https://en.wikipedia.org/wiki/Cottonwood_Limestone#Lithologic_character_and_thickness" class="extiw" title="w:Cottonwood Limestone">gallery</a> ). It was polished as a <a href="https://en.wikipedia.org/wiki/Pothole_(landform)#Grinder" class="extiw" title="w:Pothole (landform)">pothole grinder</a> in a <a href="https://en.wikipedia.org/wiki/Solutional_cave" class="extiw" title="w:Solutional cave">desolution chamber</a> of the Cottonwood (see explanation of pothole grinders in this <a rel="nofollow" class="external text" href="http://thebritishgeographer.weebly.com/river-landforms.html">external link</a>). Unfortunately, Wikipedia does not yet have an adequate article on this type of pothole formation. 
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This grinder could have been active as the <a href="https://en.wikipedia.org/wiki/Kansas_River" class="extiw" title="w:Kansas River">Kansas River</a> cut through the formation; but as it was found in an excavation of the Cottonwood <a href="https://en.wikipedia.org/wiki/Outcrop" class="extiw" title="w:Outcrop">outcrop</a>, a few hundred feet above the present river, it is very possible that this was polished by <a href="https://en.wikipedia.org/wiki/Coastal_erosion#Wave_action" class="extiw" title="w:Coastal erosion">wave action</a> of the glacial <a href="https://en.wikipedia.org/wiki/Pleistocene" class="extiw" title="w:Pleistocene">Pleistocene epoch</a> <a href="https://en.wikipedia.org/wiki/Kaw_Lake_(Kansas)" class="extiw" title="w:Kaw Lake (Kansas)">Kaw Lake (Kansas) (article pending)</a>.
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