Question about mineralization

It has been some talk about mineralization and how do they measure the amount of mineralization that is in the ground??

Off hand I know an XLT has the ability to do so and imagine a knowlegable hunter could tell by ground balancing whether he is in hot or cold mineralization...Imagine some other units may have the ability to measure the ground also...Feel free to add info...

The T2's & F75's have a bar-graph titled Fe3O4. If you do not have one of these units.......you can tell how bad the ground is....by.... how 'tight' (narrow) the "null" spot is...on the Grnd Bal knob. If there is some 'play' in the knob when you reach Grnd Bal neutral/null.....the ground is not that bad. If you have a VERY sensitive & twitchy 'sweet spot' on the Grnd Bal knob......and you can not rotate the Grnd Bal knob in any direction without instantly losing Grnd Bal.....the ground is bad.