This was basically my mining bible when I started the game. Click on the advanced mode to see the altitudes and depths that resources really thrive in. Interesting is that hard coal will spawn at any altitude… but ideally 80 blocks under the surface to be abundant. And that’s why you can find it at high altitudes if the mountains are tall enough.
You’ll see things like sapphire and topaz are a function of both altitude and depth. So to find a sweet spot for a location you need to figure out where both the ideal depth and the ideal altitude intercept. I get the impression that the luscent gems behave the same way which is why you can find lots of umbris at alt 120 in one hot spot but nearly none at the same altitude in another.