Guarding “all four corners of Forty-seventh Street between Fifth and Sixth Avenues” in Manhattan, Alicia Oltuski writes, are “two colossal diamond-shaped lamps built atop giant metallic stanchions.” They announce to all who pass by that this is the “most important quarter” of what is known as the jewelry district or the diamond district of New York, arguably the most important market in the world for the trade in “Precious Objects,” as Oltuski calls them in the title of this engaging and informative book.

Oltuski is the daughter and granddaughter of diamond merchants. She has chosen a career in writing rather than in gems, but she is understandably fascinated by the trade that has supported her family for more than half a century, and this book is the result. It is, as its subtitle indicates, at once an account of the diamond business, a portrait of the tiny, insular world in which it is conducted, and a family memoir. There are other, vastly more encyclopedic histories of diamonds — notable among them Edward J. Epstein’s “The Diamond Invention” (1982) and Stefan Kanfer’s “The Last Empire: De Beers, Diamonds and the World” (1993) — but I am unaware of a book that so intimately captures the strange and strangely beguiling place in which they are bought and sold.

On 47th Street, if not in all the world’s other diamond markets, the dominant presence is that of ultra-Orthodox Jews. The pedestrian feels, stepping off 5th or 6th Avenue onto 47th Street, as if he or she has entered another planet, if not indeed another millennium:

“The outer layers of their outfits are black and the inner, white. Black hats, black shoes, and long black coats. White shirts, white socks, and white tallis cloths, whose fringes sometimes peek out from beneath their jackets. Their sideburns are long, uncut. They walk quickly along the crowded street, as though they exist in a separate plane of reality, away from Manhattan’s busy throngs, stopping only to chat about a diamond or to glance into the window of an exchange. Some walk with their heads down and eyes averted, to keep from looking at women who might be scantily clothed, their hands behind their backs so that they won’t brush against one. They are observant of touch, guarding their flesh from contact with a member of the opposite sex. Once, at a jewelry show, a pin of my father’s caught the eye of a Hasidic woman. She was there with her husband. My father wanted to give her the pin so she could try it on, but she wouldn’t take it. At least not directly from him. He had to hand it to her husband, who passed it on to his wife.”

The “ancient customs of Judaism run deeply through the diamond business,” observed by Jews and non-Jews alike. “When two people say Mazal, short for Mazal und brucha — ‘luck and blessing’ in Yiddish — the stone has transferred possession, no matter who is physically holding the gem or what other offers the seller gets.” The Jewish connection dates back to “medieval times,” drawing upon “a history of hiding, persecution, and desperate getaways.” In the Europe of the Dark Ages, “Jews were not allowed to own land, so instead, they put their funds into diamonds — the most precious of gems. . . . Over the ages, as Jews were linked with the diamond trade, Judaism became a worldwide business system in addition to a religion. Rabbis were not just spiritual guides but international deal enforcers,” and:

‘Precious Objects: A Story of Diamonds, Family, and a Way of Life’ by Alicia Oltuski. Scribner. 356 pp. $24 (Scribner)

“The precautions Jews had to take during centuries of global persecution also set the foundation for many of today’s diamond customs. My own father’s secrecy comes from a long tradition of tight-lipped diamond dealers. For centuries, there was no choice but to be discreet. During the Inquisition and the pogroms, Jews kept their diamonds hidden in order to assure holding on to them. The diamond business was virtually a paperless world because written contracts were too dangerous. A man’s promise was safer than his signature, and trust is still the most vital component of the trade. . . . Even bargaining is an old Jewish endowment, practiced by the Torah’s superheroes. Abraham and Moses negotiated with God. Spare Sodom and Gomorrah, don’t kill the Jewish people. Sometimes they won and sometimes they lost — that’s business. If it’s all right to haggle with God, you can haggle with anyone.”

In the diamond business, “everything works on credit, loan, and trust,” and overall the system functions smoothly, but from time to time someone welshes on a deal and more generally, “while the diamond people abided by a remarkable code of ethics within the business, they were not as concerned about what happened once the diamonds left the industry and emerged in the outside world.” Anything as valuable as diamonds is certain to attract more than its share of crooks, and the diamond trade, outside 47th Street and its counterparts around the world, is no exception.

“The path of a diamond,” Oltuski writes, “from the mine to its eventual customer, can span continents and involve countless people, destroying some of them and saving others. It employs almost every faculty mankind has mastered — art, science, commerce, and force. And it always has consequences for someone, somewhere.” Thanks to the astute marketing campaign begun by Harry Oppenheimer when he ran De Beers in the 1930s and ’40s, diamonds are universally equated “with love and eternity.” Ian Fleming appropriated its slogan as the title of one of his James Bond novels, “Diamonds Are Forever.” Carol Channing first sang it in “Diamonds Are a Girl’s Best Friend.” Et cetera. The list is very long because diamonds are so deeply embedded in popular mythology as “emblems of romance and glamour.”

There’s nothing glamorous about 47th Street. Oltuski’s father’s office “is certainly no Tiffany & Co. or Cartier.” It “is starkly lit by fluorescent lighting that makes you dizzy after a full day’s work,” and “its gray carpet is hard and thin.” The diamond district exists far less to sell to retail customers — though it is open to them — than for the simple yet infinitely complex business of dealing, passing the stones from one hand to another in what amounts to a commercial daisy chain. It is not, though, an entirely random business: “In the laboratories of the Gemological Institute of America, the stones are measured, scrutinized, and given a report according to the Four Cs of diamonds, a little set of commandments that the GIA established and to which every dealer subscribes: carat weight, color, clarity, and cut.” Within those Four Cs, the number of variations appears to be literally infinite. Virtually every diamond will, under the close scrutiny of a dealer’s loupe, reveal its imperfections, but even with these, the stones can seem, and to all intents and purposes be, perfect.

Like all other worlds, the diamond trade is far from immutable. Diamonds on offer are now often posted on the Internet, the Rapaport Diamond Reporthas standardized pricing to an unprecedented degree, and fewer young Orthodox Jews seem to be entering the business. Beyond that, on 47th Street the International Gem Tower is rising, a building that may draw dealers out of their little warrens and into sleek new surroundings. “I’m not sure I prefer a district that actually looks like a place where millions of dollars of diamonds course through the streets, instead of a medieval market,” Oltuski writes, and as one who’s harbored a fondness for the diamond district for decades, I agree. But whatever changes lie ahead, Oltuski has paid fond, affecting and informative tribute to the world of her fathers.

Jonathan Yardley is the author of “Second Readings: Notable and Neglected Books Revisited.” The contents first ran as a series of essays in The Washington Post.