Locality: Sayreville, New Jersey
Mohs Hardness Scale: 2.5
Amber, AKA fossilized tree resin, is not just beautiful, but also really great for science. Despite the name, amber doesn't have to be, well, amber. It can be green, brown, bright yellow, or clear. And it's one of the best ways to learn about ancient life, especially when it comes to things that are super small or super fragile.
Here's how that happens. When a tree gets injured, it leaks sap to cover the wound, like a scab. Then some other living thing wanders past and gets stuck in the sticky goo. Over time, more sap pours out, encasing the soon-to-be-fossilized creature in a resiny tomb.
Then several million years later, researchers might get to find it and learn all about that little guy's final moments.