Mineraldle
Puzzle #55 was staurolite.
Staurolite is a reddish brown to black, mostly opaque, nesosilicate mineral with a white streak. It crystallizes in the monoclinic crystal system, has a Mohs hardness of 7 to 7.5 and the chemical formula: Fe2+2Al9O6(SiO4)4(O,OH)2. Magnesium, zinc and manganese substitute in the iron site and trivalent iron can substitute for aluminium.
What the record says
Puzzle 55 ran on 8 Sep 2026 and the answer was staurolite, played with 6 guesses against 4 columns. On the record: Crystal system - monoclinic; Strunz group - silicates; Elements - Al, Fe, H, O, Si; Named after - other.
Beyond the grid the record adds Formula - Fe²⁺₂Al₉Si₄O₂₃(OH); Named after - cross.
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
- monoclinic
- Strunz group
- silicates
- Elements
- Al, Fe, H, O, Si
- Named after
- other
Also on the record
- Formula
- Fe²⁺₂Al₉Si₄O₂₃(OH)
- Named after
- cross