What is the cheapest mineral?

Answer 1

Zircon is the oldest known mineral, at over 4 billion years, but the youngest is impossible to say. Minerals are forming all over the Earth at this very moment. You could perhaps safely say that the youngest will be found in the rock of the the latest volcanic eruption.

Answer 2

For the collector, the ones you see at the national park gift shops and the like. Usually hematite, pyrite, quartz, sometimes fluorite and calcite.

Answer 3

The smallest mineral is ground salt.