OK, scary golem like creature that can jump out of nowhere, check, hard to defeat with mundane weapons, check. Weapons break when striking it -- here's the opportunity to make this monster 'fun' (well, fun for the DM ....).
By adding a Fort save to avoid damage, each time the players strike it, you'll be calling for a saving throw -- that should create some tension/apprehension. It's a relatively easy save to make, but players will be hitting it a lot, so something is bound to go sideways in a few rounds. Adding a random table for the effects of bashing your weapon into a stone creature can be a little more dramatic than just 'it breaks', and gives characters wielding magical weapons a chance to make new decision making paradigms before their precious blade is shattered ...
stone column or statue of a woman wielding a weapon, that comes to life to
guard a tomb, treasure or doorway.
Sometimes these guardians can be found in pairs.
These guardians are often built into frescoes, columns, or the surrounding architecture, and frequently can attack with surprise.
A caryatid column will not pursue it’s foes, choosing to stay near it’s plinth, tomb or chest.
Caryatid Column: Init -1, Atk stone sword +6 melee (1d8+3); AC 13; HD 7d8+14 (30 hp); MV 25'; Act 1d20; SP automaton, resistant to non-magical weapons; SV Fort +6, Ref +4, Will +6; AL N.
A caryatid column can be created with the 3rd level Wizard spell Breathe Life (with a cost of creation being 25,000 gp, a month’s construction, and a week’s casting requiring a 36+ spell check result and knowledge of the shatter spell).
Caryatid Columns are a type of golem, and thus are immune to spells or other forces that would affect the living -- they do not eat, sleep, breathe, or have minds.
The stone guardian only takes half damage from non-magical weapons, and any weapon that strikes may take damage – roll a DC 6 Fortitude save with the wielder’s save modifier each time it is struck by a manufactured weapon; magical weapons with a bonus to damage grant that same bonus to their Fort Save. Failed saves require the wielder to roll on the chart below.
1-3 The wielder’s hand is jarred from striking solid stone – they take 1d3 hp damage.
4-6 The wielder’s hand is jarred from striking solid stone – they take 1d3 hp damage and drop their weapon.
7-8 The wielder’s weapon is not as sturdy as its stony target, and is bent or twisted – the weapon has a -1 to hit until a skilled weaponsmith can repair it (DC 15 repair). This effect can be cumulative.
9-10 The wielder’s weapon is not as strudy as its stony target, -1d to damage rolls until a skilled weaponsmith can repair it (DC 10 repair). This effect can be cumulative.
11 The weapon is dented, cracked, or otherwise compromised after striking an immovable target. Further saving throws to avoid damage to the weapon are -2 until a skilled weaponsmith can repair it (DC 15 to repair). This effect can be cumulative.
12 The wielder’s weapon breaks and is unusable. Magical weapons might be repairable by a skilled weaponsmith (DC 20 repair).