All of the symmetry – Cm: Gerstleyite

Over the long weekend (and Tuesday as well!) we've got three short posts very much inspired by the space group list project.

Every crystal structure that we've featured in the blog so far (and pretty much every crystalline solid material) has some symmetry in the way its atoms are arranged. Through the beauty of mathematics there are only 230 unique combinations of symmetry as we know it in three dimensions. So every one of our crystal structures will have a space group that describes its symmetry (which coupled with the size and shape of the box and basic unit of atoms is how we describe and build models for crystal structures).

As part of their 'Fascination of crystals and symmetry' MOOC Michael and Frank got the participants of the course to gather together a crystal structure for each of the 230 space groups. They collected these into a poster, which you can download from here, but we thought we could feature three of them!

What does it look like?

Image from the space group project list https://crystalsymmetry.wordpress.com/230-2/

What is it?

This is the structure of Gerstleyite, which crystallises in the monoclinic space group Cm and is number 8 in the list of 230 space groups. Gerstleyite is an arsenic mineral, found in sedimentary environments and is a deep red colour.

Where did the structure come from?

The structure was determined by Nakai and Appleman in 1981, and can be downloaded from the American Mineralogist Crystal Structure Database.

The 'Fascination with crystals and symmetry' MOOC will be running again from mid October – sign up here to take part! http://bit.ly/crystal_MOOC_2nd

Tags: mineral   space group   symmetry