iron-manganese concretion

例句：

1. 1. Theiron-manganese concretions are a valuable resource for mining.
   铁锰结核是采矿的重要资源。
2. 2. The discovery ofthese iron-manganese concretions has sparked interest in theirpotential use as building materials.
   这些铁锰结核的发现激发了人们使用它们作为建筑材料的兴趣。
3. 3. Due to the high concentration ofiron and manganese, these concretions are prone to corrosion.
   由于铁和锰含量高，这些结核容易腐蚀。