Chalcedony. Chalcedony. Where do I know that word from?

We were walking along in the dark, my hand gripping the hand of one of the interpreters walking in front of me. Fortunately, the floor of the massive structure we’d entered was smooth and the way flat. As long as I held on to the woman in front of me with one hand and kept touching the wall with the other, I felt pretty sure of my steps - even if I couldn’t see ahead of us, or around us, or behind us. Now I understood what...