Dripstone Crust

This chunk of Ordovician-age limestone, from near Yellville, Arkansas in the Ozarks region, shows the movement of limestone minerals by surface water. I didn't collect it, but I surmise that it was in a sheltered overhang where groundwater or rainwater dissolved calcite from the overlying limestone and deposited it as a crust while the water evaporated. Features like this are found in caves, where they take the general name of dripstone.