This week’s Facebook Mineral of the Week Group’s selected theme is equant crystals.
An equant crystal is essentially one that's roughly equal in all directions, such as a cube or octahedron.
Now while it should be relatively easy to select a mineral that forms in the isometric (also know as the cubic) system, it might surprise you that often the actual crystals are not, in fact, equant. They may have grown along one axis preferentially (such as the chalcotrichite variety of cuprite), or may be distorted or intergrown.
Many of the other crystal systems can produce equant crystals, but given that many of my specimens are small, validating this might be a challenge! As Bruce Kelley says, this theme is a little bit subjective, but he’s game for anything that illuminates a concept in mineralogy.
On that basis, here are three minerals that are trigonal, and all exhibit an equant habit. I dare you to measure them! 😆
Below: Fluor-uvite (green) and svanbergite (orange) on a magnesite matrix (pink), Pomba Pit, Brumado, Bahia, Brazil. 95mm wide.
Scientifically fascinating but also very beautiful specimen! reminds me of chopped seaweed on smoked salmon.. love the colour combo. :-))