Empress Eugénie’s 1855 diamond bow brooch, estimated at $4 million to $6 million, will be among the famous historical pieces on the auction block at Christie’s Rare Jewels and Gemstones: The Eye of a Connoisseur sale on April 15. Made by French jeweler François Kramer for the renowned courtesan who was married to Louis Napoléon, the brooch was later owned by the Astor family of New York. It’s among 155 lots that represent many historical and iconic jewels from the Art Nouveau and Art Deco periods along with important stones.

“This unique ensemble represents a walk through some of history’s most prominent figures and their jewels,” says François Curiel, Christie’s chairman of jewelry. The assortment includes a representation of the world’s great Art Nouveau jewelry designers René Lalique, Henri Vever, and Georges Fouquet, in addition to Cartier’s Mystery Clock (estimated at $500,000 to $700,000), an iconic Art Deco design in which the hands appear to float across the face. The clock is one of 12 made by the legendary young clockmaker Maurice Coüet, who collaborated with Cartier from 1922 to 1931. Christie’s is also offering a rare 14.23-carat fancy intense pink diamond (shown), estimated at $10 million to $15 million, which is extraordinary for its size and depth of color. (www.christies.com)

―Jill Newman

Last October, Sotheby’s set a world auction record when it sold a 6.04-carat fancy vivid blue diamond for $7,981,835 at its Hong Kong sale. It expects to create the same bidding frenzy when a 72.22 D-color, pear-shaped diamond hits the auction block at its Magnificent Jewels and Jadeite Sale on April 10 in Hong Kong. Bidding will start at $10 million for the exceptional-quality stone that is described as the size of large strawberry and is the largest pear-shaped D-color flawless diamond to date to appear at auction in Asia. The sale also presents a rare 3.47-carat fancy vivid blue heart-shape diamond, with an estimated value of $3 million to $3.8 million, and the world’s largest graded intense purple diamond, a 3.02-carat radiant-cut stone, with an estimated value of $1.5 million to $1.8 million. When it comes to the price of rarified diamonds, clearly the sky is the limit.  (www.Sothebys.com)

―Jill Newman

In her pursuit of rare and unusual gems, jewelry designer Cynthia Bach uncovered a large grape-size melo melo pearl, which is a rare natural orange or melon-color pearl found in marine snails in the South China Sea and the Bay of Bengal. “I have many clients who collect jewelry like art and want unusual pieces,” says the Los Angeles-based designer, who acquired the pearl from a gem dealer.  She set the 30.90-carat pearl with her signature 18-karat gold crown design adorned with orange diamonds on a pendant for $125,000 (shown). In addition to the newly unveiled melo melo pendant, Bach has introduced a Victorian-style collection for spring featuring blackened 18-karat gold jewelry in lacy patterns with black diamonds and white opal accents. (Available at Neiman Marcus Precious Jewels Salon Boston, 617.536.3660)

―Jill Newman

Jewelry designer Kimberly McDonald has taken the simple geode, which is a rock cavity with internal crystal formations, and transformed it into a striking jewel. As a longtime collector of large-scale geodes, the New York-based designer was captivated by miniature versions she discovered last year while scouting stones for private clients. “You never know what’s inside a geode rock until you crack it open,” says McDonald, who is launching her geode jewelry at Bergdorf Goodman in New York on January 28. “Each rock is so distinctive; some sparkle, some bubble, and some appear like a rainbow of colors.” Her geodes come in a full range of colors from red and pink to lavender and gray, all bearing the rough, black-rock exterior. Each piece of jewelry ($2,700 to $17,000) is designed around the geode in gold with colorful diamond and sapphire accents. (www.rockras.com)

For the opening of its 100^th boutique worldwide at 709 Madison Avenue in New York, Chopard unveiled special collections of jewelry and watches that celebrate the spirit of the Big Apple. Caroline Gruosi-Scheufele, co-president and design director, created a collection of one-of-a-kind pieces featuring an array of vibrant colored stones―such as the red sapphire, amethyst, and black diamond necklace (shown)―meant to reflect the multifaceted city. The “Happy Apple” emulates the brand’s iconic “Happy Diamond” design, but with a diamond-studded apple as the symbol in each piece. For men, Chopard designed limited-edition series of the men’s Mille Miglia GT XL and L.U.C. XP timepieces featuring midnight-blue dials and the New York City skyline engraved on the back of the case. Designed by noted French architect Thierry W. Despont, the lavish store was created to feel like an expansive private home, with white-oak wall panels and fixtures, velvet curtains and chairs, and a large fireplace, but it’s a home rich with diamond and jewels. (www.chopard.com)

―Jill Newman

Turkish jeweler Sevan Bicakci, who spent more than two decades working in Istanbul’s Grand Bazaar, celebrates his country’s rich culture and history through his artistic jewelry collection known simply as Sevan. The artist hand carves and paints gemstones, which are set in elaborate 24-karat gold rings. The colors, motifs, and iconography of each ring depict his city’s architecture, religious symbols, gardens, and the Mediterranean Sea. Some of the intricate ring patterns replicate the elaborate decorations found within Istanbul’s grandiose Topkapi Palace. Each ring design takes six months to a year to create. In November, Sevan unveiled an expanded collection of necklaces, earrings, and pendants at Barneys New York. (www.barneys.com)

—Jill Newman

Kentshire Galleries, a New York destination for antique and period furniture and decorative arts in Greenwich Village, has opened a second location on Madison Avenue. The new three-story townhouse gallery combines the company’s fine antiques with period jewelry, a first for this family-owned company. Up until now, the jewelry was sold apart from the antiques through Kentshire’s salon in Bergdorf Goodman.

To mark the opening of its uptown gallery, Kentshire unveiled an exhibition titled “Exotica: Antique Furniture, Objects and Jewelry of Unusual and Unexpected Materials” on display through January 20. The exhibit features antique jewelry made from an array of unexpected elements such as tiger’s claw, steel, and stag’s teeth, along with antique decorative objects and furniture crafted from ostrich eggs, bone, paper, ivory, fossils, and minerals.

Kentshire has a loyal following for its period jewelry, which includes a wide range of important, signed pieces such as a Cartier Art Deco diamond and cognac citrine necklace (pictured). Since 1940, Kentshire has been one of the foremost dealers of fine antique English furniture and period jewelry. Forty years ago, the second generation entered the business with brothers-in-law Fred Imberman and Robert Israel. The duo built a world-class inventory of Queen Anne, Georgian, and Regency furniture and decorative arts. In the 1980s, the partners’ wives developed a flourishing antique-jewelry business and opened within Bergdorf Goodman. The expansive 3,500-square-foot uptown gallery represents the next era for this family business. (212.421.1100)

—Jill Newman

When Leviev opened its first US salon on Madison Avenue in mid-November, it unveiled more than 5,000 carats of exceptional white and colored diamonds, including two extremely rare red diamonds, a 51-carat D-flawless diamond ring, and several elaborate designs over $10 million each. As the world’s largest diamond-cutter and polisher to the trade, owner Lev Leviev reserves his best cache of stones for his own stores on London’s Bond Street and New York. Leviev’s diamond-rich neighbors on the block include Graff, Chopard, and Ivanka Trump Jewelry, among others. The two-story boutique is located in a 1920s historic landmark building at 700 Madison Avenue. (877.4.LEVIEV, www.leviev.com)

—Jill Newman

A spectacular strand of natural pearls is expected to cause a stir when it’s unveiled at Sotheby’s Magnificent Jewels auction in New York on December 4. Aside from its beauty and rarity, the necklace has a well-traveled, fascinating provenance: The Cartier, Paris-designed necklace belonged to HRH Queen Mary, who gifted it to her son the Duke of Windsor, who gave it as a token of love to his wife, and it was sold at a Sotheby’s Geneva auction in April 1987 to Calvin Klein for his then-wife, Kelly. Natural pearls are exceptionally rare and are commanding record-breaking prices at auction. The necklace is estimated from $1.5 million to $2 million, but insiders expect it will fetch much more. (212.606.7176, www.sothebys.com)

—Alyson Gerber

Diamond house Harry Winston has collaborated with menswear designer Thom Browne on a line of understated diamond jewelry for men, the Harry Winston Men by Thom Browne collection. While many men prefer to see glittering diamonds strictly on women, this distinctive array gives them a reason to reconsider. In keeping with the refined, modern tailoring of Thom Browne’s menswear, the sleek white gold rings, cufflinks, and ties bars are defined by custom-cut trapezoid diamonds set in narrow diagonal rows reminiscent of the regiment stripe. The collection, introduced in the jeweler’s Fifth Avenue flagship in October, includes $8,000 diamond pavé cufflinks and a limited- edition $42,000 pavé diamond watch with blue sapphire and red ruby diagonal stripes across the face. (800.988.4110; www.harrywinston.com)

—Jill Newman