Oh, yeah! Jewel Cave is a bit unique in this regard. There's a lot of sparry calcite (large, well-formed crystals) inside the cave. The difference is in the si

Oh, yeah! Jewel Cave is a bit unique in this regard. There's a lot of sparry calcite (large, well-formed crystals) inside the cave. The difference is in the size and shape of the crystals. Large crystals like that can only form when they have lots of room to grow (i.e. when everything is underwater). Those formed while the cave was flooded with water that was over-saturated with calcium carbonate. The rate of growth of a calcite crystal is a lot faster (inches per decade) under those conditions. The speleothems that are forming today grow slower (inches per century) because they're precipitating from a very thin layer/drip of water that only becomes saturated when it starts to evaporate or flow differently. Both processes are very rapid in geologic terms, but there's a significant difference in rate between the two.