Crystallization of the skin, and subsequently the rest of the body, is a symptom of "Mekstrom's Disease," in George O. Smith's 1956 novel Highways in Hiding, (alternate title The Space Plague) which also features ESP and telepathy.
The protagonist, Steve Cornell, is an esper, which means he can sense physical things with his mind - he can "dig" things that he can't see, in other rooms, and on the highway he can check the road hundreds of metres ahead, allowing him to drive really fast. His finance, Catherine, is a telepath, which means she can sense thoughts, but not things.
Mekstrom's disease is effectively a crystallization of bodily tissues:
"The difference lies in the structure. By X-ray crystallographic methods, we have determined that Mekstrom’s Flesh is a microcrystalline formation, interlocked tightly.” Scholar Phelps looked at me thoughtfully. “Do you know much about crystallography?"
The people who turn out to have been treated to survive Mekstrom's Disease are very strong, and very, very durable:
"Sure. Consider what a man might be if he were Mekstrom's all the way through."
He nodded. "You, would have a physical superman," he said. "Steel-strong muscles driving steel-hard flesh covered by a near impenetrable skin. Perhaps such a man would be free of all minor pains and ills. Imagine a normal bacterium trying to bore into flesh as hard as concrete. Mekstrom Flesh tends to be acid-resistant as well as tough physically. It is not beyond the imagination to believe that your Mekstrom Superman might live three times our frail four-score and ten. But—"
Even a gunfight among groups of Mekstrom survivors is rather pointless:
Their rifles came up and yelled at one another like a string of firecrackers; they wasted a lot of power and lead by not taking careful aim. One of them emptied his rifle and started to fade back to reload, the other let him have it in the shoulder. It spun the guy around and dumped him on his spine. His outflung hand slammed his rifle against a tree, which broke it.
He gave a painful moan and started to crawl back, his arm hanging limp-like but not broken. From behind me came a roar and a pattering of shotgun pellets through the trees; it was answered by the heavy bark of the 35-70 Express.
I’m sure that in the entire artillery present, the only rifle heavy enough to really do damage among these Mekstroms was that Express, which would actually stop a charging rhino. When you get down to facts, my Bonanza .375 packed a terrific wallop but it really did not have the shocking power of the heavy big-game rifle.
Motion caught my perception to one side; two of them had let go shotgun blasts from single-shot guns. They were standing face to face swinging their guns like a pair of axemen: swing, chop! Swing, chop! and with each swing their guns were losing shape, splinters from the butts, and bits of machinery. Their clothing was in ribbons from the shotgun blasts. But neither of them seemed willing to give up. There was not a sign of blood; only a few places on each belly that looked shiny-like.
The treatment to survive Mekstrom's is indeed very painful. Because the (unchanged) heart can't pump blood into crystallized tissue, it dies, and the body goes into fatal shock when the organs of the abdomen crystallize and toxins can't be eliminated from the body.
"[...]the infection reaches the lower parts of the body. I believe you can imagine the result, elimination is prevented because of the stoppage of peristalsis. Death comes of autointoxication, which is slow and painful.”
The treatment consists of using multiple IVs drilled into the converted tissue to keep the extremities alive, while similarly using shunts to keep the core alive.
"I'll not fool you," he said drily. "This is going to hurt."
He set the skin-blast hypo on top of the joint and let it go. For a moment the finger felt cold, numb, pleasant. Then the shock wore away and the tip of my finger, my whole finger and part of my hand shocked me with the most excruciating agony that the hide of man ever felt. Flashes and waves of pain darted up my arm to the elbow and the muscles in my forearm jumped. The sensitive nerve in my elbow sang and sent darting waves of zigzag needles up to my shoulder. My hand was a source of searing heat and freezing cold and the pain of being crushed and twisted and wrenched out of joint all at the same time.
And as the disease progresses, more intervention is necessary and more pain is involved:
At those few times when my mind was clear enough to let me use my perception, I dug the room and found that I was lying in a veritable forest of bottles and rubber tubes and a swathe of bandages.
Utterly helpless, I vaguely knew that I was being cared for in every way. The periods of clarity were fewer, now, and shorter when they came. I awoke once to find my throat paralyzed, and again to find that my jaw, tongue, and lower face was a solid pincushion of darting needles of fire. Later, my ears reported not a sound, and even later still I awoke to find my- self strapped into a portable resuscitator that moved my chest up and down with an inexorable force
The disease was named after the space-tech who was the first known victim, though it's not actually clear if it came from space or not:
Otto Mekstrom had been a mechanic-tech at White Sands Space Station during the first flight to Venus, Mars and Moon round-trip with landings. About two weeks after the ship came home, Otto Mekstrom's left fingertips began to grow hard. The hardening crawled up slowly until his hand was like a rock.
You can check out a gallery of covers in case you recognize one of them.
The novel was serialized in Imagination in 1955; you can read the story in the March, April, May and June issues at the Internet Archive (which is where I got these quotes).