Emerald and diamond ring by Raymond Yard, set with an octagonal step-cut emerald of approximately 18.04 carats, sold for $5,511,500.

NEW YORK CITY — Harry Winston bought the Rockefeller Emerald for a record price per carat at Christie’s on June 19.

The luxury jeweler’s chief executive officer, Nayla Hayek, had instructed chief financial officer Robert Scott to “bring this magnificent gem home at any price,” Christie’s reported. That price was $5.5 million, setting a world record of $305,516 per carat for an emerald at auction.

Christie’s offered the octagonal, step-cut, 18.04-carat emerald ring on behalf of a private American collector, who had owned it for more than a decade. John D. Rockefeller Jr acquired the stone in 1930 as the centerpiece of a brooch for his wife, Abby Aldrich Rockefeller. When she died in 1948, their youngest son, David Rockefeller, inherited it and instructed designer Raymond Yard to set it in a ring. The piece later passed from the family into private ownership.

“Harry Winston is immensely proud to own the finest emerald in the world, which once belonged to one of America’s most important dynasties,” Hayek said.

The acquisition comes less than a month after the jeweler spent $8.9 million, or $2.2 million per carat, on a fancy vivid blue diamond at Christie’s Hong Kong.

Christie’s Magnificent Jewels auction fetched a total of $26.1 million, selling 83 percent by lot and 89 percent by value.

Other jewels at the event included a modified lozenge mixed-cut, 5.01-carat, fancy deep grayish-bluish-green, VS2-clarity diamond, which found a buyer at $4.4 million, or $876,547 per carat. A round brilliant-cut, 16.11-carat, D-color, flawless diamond went for $1.9 million, or $119,646 per carat.

The results “underscore the strength in the market for pieces of the highest quality,” said Tom Burstein, Christie’s head of jewelry for the United States.

Prices reported include the buyer’s premium   For information, 212-636-2000 or www.christies.com.