An ingratiating, unsentimental introduction to New York City's multibillion-dollar diamond industry--a warren of fevered activity on West Forty-Seventh Street. With the exception of setters (mostly of Italian extraction), the diamond people--for whom Schumach has obvious affection--are predominantly Jewish, fiercely competitive, habitually secretive, and unfailingly honorable. Millions of dollars worth of stones pass on consignment with little more than a handshake and the Yiddish words ""mazel und brucha,"" luck and blessing. (The scanting of formal records also helps, of course, to keep tax collectors at bay.) But however ghetto-like their enclave, the diamond people are world-class globe-trotters, dashing off at a moment's notice to London, Antwerp, Moscow, Tel Aviv, or a smuggling center such as Monrovia, Liberia. Members of the exclusive Diamond Dealers Club, which serves as a sort of ad hoc bourse and arbitrates commercial disputes, stand at the top of the district's pecking order; but Hasidic curb brokers, mechanics (cleavers, sawyers, cutters, girdlers), booth merchants, carriage-trade retailers, and lesser lights belong in the fullest sense of the word to a close-knit fellowship. Its sense of fraternity, Schumach reports, was brutally violated in 1977 when a young dealer named Pinchos Jaraslawicz was murdered and robbed by renegade colleagues. This breaching of the ""mazel und brucha"" code by insiders outraged the diamond people (no strangers to criminal violence in their travels). Significantly, however, it was the code, plus the community's sharp eye for transactional detail, that led to the slayers' identification. There are, of course, stones for which anyone might kill--e.g., the Koh-I-Noor, Hope, or Sancy. Schumach offers brief histories of these legendary gems, provides background information that puts Forth-Seventh Street into perspective as a hub of the international jewelry trade, and notes the public's fast-growing fascination with diamonds as a hedge against inflation. But the parochial mores of the diamond district are Schumach's preoccupation--and he does very well by them indeed.