Looking at the shiny black stone on the desk, Nightingale asked, "What's this?"
"Obsidian." Roland even did not raise his head, busy with painting his blueprint.
"Ob... What?"
"No, I was talking nonsense." He sighed. Just by looking at its shape and color, how could he know what it was? After all, he was not a geologic expert, and could not guarantee to distinguish even a pure metal, to say nothing of ores. The knowledge he had in his head only told him most ores were compounds with complicated compositions and their color varied with different impurities. For example, iron ores could be divided into hematite, pyrite, and siderite, which looked totally different from each other. Especially the pyrite, which would sometimes show a light yellow metallic sheen, was often wrongly identified as gold, giving it a nickname "Fool's gold".
