Thanks for playing! I'm pretty sure that's the oldest possible rock. Here's how age works:
- Color is a random number between 1 and 9.
- Grain is a random number between 1 and 10.
Color is worth 100 per point while grain is worth 20 per point. That's why you can pretty frequently encounter scenarios where a very grainy rock is older than a somewhat-grainy rock of the next highest color.
...At least, the ranges are supposed to look like that but I couldn't properly dial the color value in before I hit time. That's why there's a light green rock in the tutorial but not in the game :P

