The canvas below shows two views of the crystal structure for cordierite (chemical formula Mg 2 Al 4 Si 5 O 18 ), a gem mineral we haven’t explicitly…

The canvas below shows two views of the crystal structure for cordierite (chemical formula Mg2Al4Si5O18), a gem mineral we haven’t explicitly covered, but which is in your textbook (p287) and is also known as iolite. The top image is oriented to be looking along the a-axis (or across c-axis), and the bottom image is oriented to be looking along the c-axis (or across the a and b axes) but in a slightly oblique manner. Interestingly, this crystal structure allows Si and Al to reside randomly within the same polyhedra, and so are often listed together as “(Al,Si)O4”. Based on the relative abundances of cations in the mineral formula and their coordination numbers, follow the steps given below to label or sketch these features:

  1. A.The polyhedra that represent (Al,Si)O4groups
  2. B.The polyhedra that represent MgO6groups
  3. C.The location of basal cleavage
  4. D.The location of the structure’s channels

the photo cannot be download so here is a link to the assignment

https://gyazo.com/6febbc7c08c714a3f658d7c40408a360