April 2024 - Topaz

April 2024 - Topaz

  • Locality: Thomas Range, Utah
  • Chemical Formula: Al2SiO4(F,OH)2

Topaz is the one of the hardest minerals on the Mohs scale, but that doesn’t mean they’re the most durable. And it’s all thanks to the topaz’s cleavage.

No, not that cleavage. For rocks, it means their tendency to crack along well-defined planes. Topaz has “perfect” cleavage thanks to its crystal structure. The atoms are well bonded in some directions, but only weakly attached in others. So one good hit, and … crack.

Topaz is a silicate-based mineral that also includes aluminum and fluorine.

It’s one of the first stones that humans used as gemstones, and they come in just about every color you can think of.

The topaz crystals in this box are still embedded in volcanic rhyolite from the eruption that formed them 6-7 million years ago.

See all articles in List of Rocks