On-line glossary of Physical Geology by Charles C. Plummer and David McGeary will help you to explain geological terms used in your courses.

On-line Geological English-Czech Dictionary will help you to translate more expressions.

For pronunciation use :

• Lingea Lexicon - good and fast available on CD, in our classrooms and study rooms in IC.
• J. Fronek´s dictionary or Velký anglicko-český slovník, Leda nebo nebo dřívější Academia
  
• For general English Longman On-line Dictionary and many others can help you.