第10話: 地質学者が放棄されたマンガン鉱山を調査し、有毒なロドノライトバラストを発見

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The geologists set out for a historical manganese mine, with Yoko hesitantly in the lead, after Nagi has to miss out due to a last-minute excursion. We learn some properties and uses of manganese. Blocked by a collapsed rail tunnel, the team searches for fallen samples along the tracks. They discover rhodonite and rhodochrosite in quantity, suggesting prohibited use of potentially toxic tailings as track ballast. Perhaps a long-ago rail crew used their cargo for emergency repairs, though the actual answer remains unknown. (Source: Wikipedia)