User blog comment:Obsideon/RARITY?/@comment-4583259-20120219062452

My page on relative abundances of materials should help somewhat. I'm only counting the number of blocks, not compensating for whether they're easy to find or not.

For example, on that page you'll see that Blue_Stone, Sulphur Ore and Feldspar are just about the rarest materials of all. However, most people who play the game think that Notchium ore is the hardest to find. This is because Notchium is often underground where it cannot be seen, but the Feldspar etc. are on the tops of really obvious colorwood trees.