Voknar crystals - Highly dense crystals containing compressed energy. It is believed that the energy contained within is a remnant of the energy from the creation of the universe. The color of the crystal represents the size and energy level. Colors range from red through blue, with blue being the strongest.
"The Hitchhiker's Guide to the Galaxy. It's a sort of electronic book. It tells you everything you need to know about anything. That's its job."
Arthur turned it over nervously in his hands.
"I like the cover," he said. "'Don't Panic.' It's the first helpful or intelligible thing anybody's said to me all day."