I have 2 of that same necklace but longer. The stone is Chrysocolla.
One says Mexico SHC 925, the other is stamped just as messy as yours but I can make out SHC 925 and Sterling, there is no SHC listed in the hallmark book but there are more unknown makers than known ones,
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With no eagle mark it likely dates pre-1948 but since there is so little room for a mark the eagle was sometimes left off.