Joe and I went to an azurite mine while in Moab, Utah. We spent half a day hunting for these rich blue stones, they called the round ones blueberries. The picture below is what we found, still very dirty. The picture above is what they look like after I tumbled them.
Here is the different in one picture.
I'm keeping them in a yellow bowl for great contrast.
You can see a few green pieces of malachite. This mine was privately owned so we paid a guide to take us and it was so much fun! This bright color is caused by the weathering of copper ore deposits. On the Mohs scale it is a 3.5 to 4 so it's very soft and fragile. And for centuries it has been used as a pigment.