Hi kobnut, I only got so far with this before going out and I'm on my phone not having it in front of me. However, to make sense of the grid entry of 18a and the other 14 like affected, my interpretation of the preamble is once you have the answer, 1 letter is extracted and the grid entry is made up of the remaining letters; possibly an anagram not just an extraction. Here enargite (as you thought, near* + gite) and the grid entry could be granite if an "e" is surplus.