The phrase "a crumbling stone" is correct and usable in written English.
It can be used to describe a stone that is deteriorating or breaking apart, often in a poetic or descriptive context.
Example: "As I walked through the ancient ruins, I stumbled upon a crumbling stone that seemed to tell the story of a long-lost civilization."
Alternatives: "a decaying rock" or "an eroding stone".
Blahyi walked past them to a crumbling stone wall overlooking a bridge.
On the far side of the field, a crumbling stone wall was covered in a thick carpet of moss.
Tourists in Nicosia's old town can eat at the Berlin Wall Kebab Shop, abutting a crumbling stone section of the dividing line.
The ruined castle complex, surrounded by a crumbling stone wall, contains such oddities as sauna baths and a dozen lion cages.
This is John Voigtmann, an American expat who turned a crumbling stone barn into La Bandita, an eight-room boutique hotel that sits atop the most-photographed of those cypress-lined roads.
The balcony overlooked an unkempt but charming park, with a crumbling stone wall at one end, where an old woman was feeding birds, and a playground at the other.
That program includes "The Tower," Quirine Racké and Helena Muskens's eerie split-screen visitation with three generations of bohemians who live in a grand, crumbling stone ruin.
On their first official shopping trip, in November 2004, they visited Casperia, a hilltop hamlet 40 miles north of Rome, and fell in love with the shell of a place — crumbling stone walls, antiquated beams and all.
As the traveler heads out onto a blustery promontory jutting into the ocean and begins to descend, expanses of ocean — 500 feet below — sweep past the car windows, and the road veers impossibly close to the edge, meandering between a face of gray, crumbling stone and a precipitous drop to the sea.
He was at the very pinnacle of his dream, the river dressed in its currents, the deep hole under the cut-bank, and the fish like silver bullets swarming to his bait, when they woke him — when Rob woke him, Rob Greiner, his roommate, Rob with a face of crumbling stone and two policemen there at the door behind him and the roar of the dorm falling away to a whisper.
On August 8 La Pérouse arrived at Prince of Wales Fort, an impressive but crumbling stone fortress that was defended by 39 civilians.
