Plant samples unlock at level 2, fossil samples unlock at level 5, and crystal samples unlock at level 8. This will unlock the ability to take and analyze samples. To complete this collection, you’ll need a microscope, high Logic skill, and some plants, fossils, crystals, and metals to take samples from.
When you find a fossil in a rock, you’ll need to extract it by clicking on it in your Sim’s inventory. Just keep digging up those rocks and hoping for the best. There’s no strategy or pattern to follow to ensure you get specific ones.
Like the other collections that are found in rocks, fossils are a pretty random find. The rodent cages even have their own little corkboard to display all the postcards your rodent brings you. The postcard is random but you can receive all 7 postcards from the same rodent. Your rodent will occasionally go on adventures by themselves and will bring you a postcard from their travels when they return. These postcards can only be obtained from your pet rodent.
Using this option will always give you a MySims capsule, so if you are hunting for MySims, specifically, use up any and all treasure maps you find. This treasure map will open up the “Dig for Treasure” option on other rocks. Sometimes, you may receive a treasure map from digging up a rock. Whenever you dig up a rock and receive a capsule, you have a MySims trophy! Click the capsule in your Sim’s inventory to open it and see which MySims you got.