煤结核

例句：

1. 1.The mine manager discovered a significant amount of coal nodules in the underground.
   矿经理在地下发现了大量的煤结核。
2. 2. Coal nodules are formed by the accumulation of organic matter within the coal seam.
   煤结核是由煤层中有机物质的积累形成的。
3. 3. Due to their high value, coal nodules are often targeted for illegal mining activities.
   由于其高价值，煤结核常成为非法采矿活动的目标。