Mineraldle
Puzzle #75 was corundum.
Corundum is a crystalline form of aluminium oxide typically containing traces of iron, titanium, vanadium, and chromium. It is a rock-forming mineral. It is a naturally transparent material, but can have different colors depending on the presence of transition metal impurities in its crystalline structure.
Read about it on Wikipedia →
What the record says
Puzzle 75 ran on 28 Sep 2026 and the answer was corundum, played with 6 guesses against 4 columns. On the record: Crystal system - trigonal; Strunz group - oxides-hydroxides; Elements - Al, O; Named after - other.
Beyond the grid the record adds Formula - Al₂O₃; Mohs hardness - 9; Named after - ruby.
Mineraldle builds its record from Wikidata - CC0 1.0. The description above comes from the same place the game credits on every reveal: English Wikipedia verbatim extract, CC BY-SA 4.0. The puzzle itself is still playable in the archive, and every answer that has been and gone is listed on the past-answers page.
How it scored
- Crystal system
- trigonal
- Strunz group
- oxides-hydroxides
- Elements
- Al, O
- Named after
- other
Also on the record
- Formula
- Al₂O₃
- Mohs hardness
- 9
- Named after
- ruby