We'd like a fun, quirky play on a teacher's grading marks. They'll run from A+ to F, with all the ranges in between (A+, A, A-, B+, etc.), but each one will be textured a different way. A+ will be diamond studded, while A will be gold, B will be silver, C will be bronze, D will be tree branches (? or some other suitable metaphor) and F will be dirt. The + and - signs will be a bridge to the next material. For example, D+ would be a D made of sticks, and a + made of bronze. The style needs to be (for lack of a better descriptor) web 2.0. Inspirations include the Crystal Icon Set, located at http://www.everaldo.com/crystal/?action=preview.
Let us know if you need clarification.
We might have more icon design projects in the future; we'll be more willing to award those to the designer we pick for this contest.