Diamonds may be a girl's best friend, but next month is all about men designing and collecting some of the world's greatest gems. The Paris-based Joel Arthur Rosenthal, known professionally as JAR - an acronym synonymous for more than 35 years with ne plus ultra jewels fashioned into spirals, flowers and butterflies - will unveil his first American retrospective, "Jewels by JAR," at the Metropolitan Museum of Art in New York. Meanwhile, Sotheby's will showcase the rarest pieces made by the retired Alexandre Reza, in addition to designs by his son Olivier, with an exhibition, "The Extraordinary Jewelry of Alexandre Reza." Finally, Sheikh Hamad bin Abdullah Al Thani of Qatar boasts an unparalleled private collection of Indian jewels spanning the past 400 years - from handcrafted jade daggers of the Mughal courts to emerald turban ornaments favored by 19th-century maharajahs - which have been bound into a beautiful tome. "Jewels by JAR" at the Metropolitan Museum of Art in New York, Nov. 20 to March 9. "The Extraordinary Jewelry of Alexandre Reza" at Sotheby's New York, Nov. 1 to Nov. 13. "Beyond Extravagance: a Royal Collection of Gems and Jewels" (Assouline), $250.