precious stone
瑯 centers on a precious stone, specifically a type of gem or jewel-like mineral.
瑯 combines 王 (jade/gem) with 郎, which likely contributes the sound ロウ. The character is used for a precious stone, following the common pattern of gem names with the 王 radical.
The left side 王 (jade) tells you it's a precious stone, and the right side 郎 looks like a nobleman admiring a gem. Picture a lord holding up a sparkling jewel.
For ロウ, imagine a row of precious stones lined up on a velvet cloth: row -> ロウ, and each stone gleams like a jewel.
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