Im trying to find a rare movie from the 1980's(83' - 87'). It was broadcast on the USA network. I have seen it twice but cant remember its title. It started off in a cave with these college friends, they are exploring the cave. They come across some wierd purple crystals, which seem to be alive. Im not sure what happens next but they leave the cave. People start to disappear and stuff. We hear really weird noises, but we never see whats causing the noises. Thats about all I remember about the movie. Any help would appreciated.