Well.. Some rocks are definitely shiney. It would be interesting to see if monkeys have any affinity for well polished rocks with pretty colors. Humans do like them, maybe not as much as crystals but they're nice nonetheless.
While the ancient Romans liked transparent crystals, especially emeralds and beryls, they were not the most valued gems.
The most valued gems in Ancient Rome were the higher-quality varieties of noble opals and pearls, which are not transparent, but which show a variable play of colors, depending on the ambient light and on the angle of sight.
Why? Crystals are pretty, rocks are not. We clearly prefer shiny colorful things to dull beige things, even if shiny things are abundant.