Gemstones are pretty friggin' awesome. So many colours, so many swirls. Different transparencies, different designs. Different shapes, different sizes.

Rocks in general are awesome.
You have rough ones - untouched by the flowing currents of water - the smooth ones that are brushed by these waves - shiny ones that have been polished by a curious adventurer - dusty ones that have been forgotten by old adventurers - and so on.

Rocks hold so many secrets, esp amber - containing DNA
Rocks are the foundation for so many buildings and natural structures 
Rocks can be used as tools, channel stones, or simply decorations.