The character 瑙 is used almost exclusively in the word 玛瑙 (agate).
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usage
瑙 is a bound morpheme - it essentially never appears alone. It only shows up in 玛瑙 (agate) and rare transliterations. The 王 (jade) radical signals that it belongs to a precious-stone word family.
Left-side jade radical - written as 王 on the left, but read as 玉 (jade), the indexing radical. Marks 瑙 as a precious mineral: the second half of 玛瑙 agate, a banded chalcedony semi-precious stone. The same radical heads 玛 agate, 珍 precious, 珠 pearl.
Upper-right 巛 - three flowing strokes that originally represented hair or stitched seams on top of a skull. In the right half of 瑙 (the same shape that anchors 恼 annoyed and 脑 brain), it caps the head outline below. Read it as part of the brain glyph, not as 'streams'.
Lower-right 囟 - the soft fontanelle on a baby's skull, with seam-lines inside the enclosure. Supplies the sound: xìn drifts to nǎo through the same phonetic alternation running 恼 annoyed and 脑 brain. Together with 巛 above, this whole side is the 'brain' shape from 脑.
