Barely used alone today; it survives in the proverb 打破砂锅璺到底 — the crack runs right to the bottom, a pun on 问到底 (to get to the bottom of a question). The radical at the foot is 玉.
memory
Think of a fine 玉 piece with a thread-thin fissure: it has not broken apart, but the flaw runs all the way through — that is a 璺.
The jade radical 玉 at the foot files this under jade and stone. It points to the surface that cracks — fine jade, porcelain or glass that fissures without falling apart.
phonetic
釁xìn
fissure; quarrel (phonetic top)
The dense top is the 釁-type element meaning a split or rift. It both hints at the meaning (a crack) and historically steered the wèn reading; it is not a productive everyday phonetic.
