In the appendix, this article has copies of the original rubric and the revised rubric used for online discussions. Each of them have the following 4 criteria:
- Communication Proficiency
The descriptions for the various levels of proficiency for each of the criterion are quite good.
Ann M. Sloan and Nikolaos. “Development, Implementation, and Evaluation of a Grading Rubric for Online Discussions.” MERLOT Journal of Online Learning and Teaching, volume 7, number 4 (December 2011).
The full article is available here.