This may be due to changes in how FileMaker 11 indexes data compared to how it did it in FileMaker 7. I don't recall when the change took place, but older versions would successfully match "quartz" to "quartz." or "quartz " (last example has a trailing space).
In fileMaker 11, these values will not match.
Thus, you may need to inspect the data in your mineral name fields to see if they truly match or if small differences such as punctuation characters or spaces might be keeping them from matching.
PhilModJunk nailed it!
I'm not a "newbie" but I'm a hobbiest, definitely not a professional, so my struggles weren't quite over. I'll spell out what I did in case it might help someone else.
My related field, call it "R", a text field, contained trailing spaces for the majority of entries *. In the field manager I created a calculation field ("C") containing the Trim function: "Trim (R)". That stripped off the trailing spaces (from about 4400 of 4500 entries!) Then I deleted "R" and renamed "C" as "R".
The file was clean and I was sure it was going to work, but still the fields from the related DB were empty. ;-(
The clue on the database table manager was that even though I'd put in the proper fields, there were no records in the table: I'd neglected to import the records from the related DB. With that everything is working again, and I haven't lost data that I've been entering for 9 years.
One other observation that may help someone else: watch for the option that allows you to preserve formatting as you import. This was key for me because there were hundreds of complicated chemical formulae with suprascripts and subscripts that would have been agonizing to reproduce.
Good luck, and thanks again to PhilModJunk!
* I have no idea how those trailing spaces got there.
If there are no recors in the re-created table, then you have no data to which to link records. I can't tell from here how you ended up with an empty table. Do you have backup copies?