In reply to Andy Can:
I was a Head of Biology at a Sixth Form College for many years (not at Stourbridge), so I do have some expertise ~ might I suggest the following:
Use the Geological Society guidelines, and obviously describe the incident, maybe including photographs of the damage. Put this in writing to the Principal of the College, emphasising the poor example set to the Geology students,and make it clear you would like some feedback of action taken. Keep it all factual. Events, dates, times, place, grid references, will all ensure that they know you are serious and demand to be taken seriously.
I am very concerned that you say his students were laughing at your concerns.
Make it clear that you would like the students to have the Geological Society guidelines reinforced to them by a member of the Senior Management Team, perhaps a Vice Principal in charge of Curriculum.
For good measure, send a copy of all this to the Chair of the Governors (just address it to the Chair of Governors at the College address), making it clear that you expect feedback from the Principal.... this may encourage the Chair to follow it up, as he / she might expect further correspondence from you should you hear nothing.
As other posters have said, schools and Colleges are terrified of bad publicity, and I would be fairly confident that the Principal's and Chair of Governor's first thoughts would be in this direction.
You may consider contacting the President of the Students Union at the College. A sensitively worded letter again emphasising the poor example that the Geology students may take into their future education / careers ie play on the student welfare string with this approach.
It is a bit of a mission to do all of this, but hugely worthwhile and hopefully fulfilling.
Last course of action if you don't receive any feedback: contact their local press, contact the relevant Examining body.
Hope this helps.