掘り出す

1. Origins, structure, and basic meaning

• Structure: 掘り出す combines 掘る, to dig, with 出す, to bring out.
• Basic usage: It is used both for digging a stone out of the ground and for discovering a valuable object in a shop.

2. Common pitfalls and similar expressions

• 掘る and the result
  • 掘る focuses on digging; 掘り出す focuses on bringing something out as a result. The rare-plate example uses discovery figuratively as a kind of unearthing.