Colorful "rocks" found in a Georgia yard

From the discussion thread at the whatsthisrock subreddit:

OP, that looks like cement-solidified-and-stabilized industrial waste, possibly from dye, glaze, or pigment manufacturing.

Going back to the 1950s, manufacturers have mixed their hazardous wastes with concrete to solidify and bind it to prevent it from migrating off-site or into waterways, and to allow it to be disposed of as solid waste. I can clearly see a thin layer of plain cement on the bottom and top of those pieces. Industrial dyes and pigments back in the 20th century contained manufacturing by-products like dioxins and toxic heavy metals used as colorants.

Please err on the side of safety and dispose of whatever you collected. It could be very old and full of bad stuff. If the in situ concrete is breaking up, perhaps call the county environmental agency to let them know.