.......... You'll get much better results in a Pristine reserves system - the fringes of the bubble are best for these.
If you have space, add a prospector limpet to your set up.
That will allow you to check what is in an asteroid BEFORE you start mining it ...
Using the prospector (widget/finggy/controller) fire a limpet at an asteroid.
Target the limpet (either on it's way, or after it attaches).
The mineral composition of the asteroid will show in one of the bottom panels (forget which one) to when the limpet attaches.
Another exception is the one the OP was asking about Cobalt, a metal, is found in rocky rings.There are a couple of exceptions to the rule (e.g. Painite is a Mineral but only appears in Metallic rings), but you'll figure those out as you go along.
Many thanks for all the answers.
I want to use as less as possible external tool as edtools.ddns.net (even I like it as very useful). As a part of gameplay, I want only depend what I got in the game.
So try imagine, I am in the system far away, and I need to find (on the map) systems with asteroids belts or planets with the rings. Is there any function on the map, so I could click on it (like eg commodity >> minerals >> colatan), so I could easily find it, or I need to click on any system nerbay (on the map) and read desription?