At the 58th Grammy Awards in 2016, Carrie Underwood arrived wearing a jewel that was difficult to ignore: a ruby-and-diamond necklace centered by an approximately 12-carat vivid yellow flawless diamond known as the Firefly Diamond. Created by jeweler Johnathon Arndt, the piece was designed as a deeply personal Valentine’s gift from Underwood’s husband, Mike Fisher, and was named in reference to her song “Heartbeat.”
The necklace was conceived not simply as red-carpet ornament, but as a one-of-a-kind composition intended to feel timeless. Underwood, Fisher and Arndt collaborated on the design, pairing the intense warmth of the yellow center stone with Burmese rubies and brilliant white diamonds in a dramatic setting that balanced romance with unmistakable scale.
According to Johnathon Arndt, the finished necklace incorporated more than 20 carats of rubies and over 16 carats of white diamonds in addition to the central Firefly Diamond, bringing the total gemstone weight to more than 48 carats. The proportions alone made it exceptional, but the visual contrast was what gave the piece its identity: vivid yellow at the center, saturated red throughout the necklace, and flashes of white diamond brilliance tying the composition together.
The Firefly Diamond itself served as the focal point. At roughly 12 carats, with vivid yellow color and flawless clarity as described by the jeweler, it had the presence of a collector’s stone while still functioning within a highly theatrical piece of wearable jewelry. Rather than allowing the center diamond to stand alone, the design surrounded it with rubies and diamonds in a way that amplified the color and made the necklace feel more architectural than delicate.
Underwood completed the Grammy look with Johnathon Arndt diamond stud earrings, allowing the necklace to remain the clear centerpiece. On a night defined by high fashion and high jewelry, the piece stood out because it combined celebrity glamour with a private story about marriage, music and personal symbolism.
That personal element made the jewel more interesting than a conventional red-carpet loan. Underwood later spoke about the necklace as a Valentine’s gift from Fisher, joking that she could just as easily wear it at home in sweatpants while making dinner. The comment undercut the formality of the piece in the best possible way, giving something extravagant a sense of intimacy.
The name “Heartbeat” added another layer. Underwood’s song of the same name was current at the time, and the necklace was presented as an extension of that romantic theme. The Firefly Diamond became the emotional and visual center of the design, turning the jewel into something closer to a personal emblem than a purely decorative accessory.
The piece also reflected Johnathon Arndt’s long-standing place within celebrity jewelry, where custom commissions often sit at the intersection of craftsmanship, symbolism and spectacle. In this case, the design was not subtle, nor was it intended to be. It was built to command attention under red-carpet lighting while still carrying enough personal meaning to matter beyond a single appearance.
The Firefly Diamond did not disappear after the Grammys. Later in 2016, the stone was again associated with Underwood around the CMA Awards, reinforcing its status as more than a one-night showpiece. That continuity gave the jewel a life beyond the original event and helped cement its place among the more memorable celebrity jewelry moments of the decade.
Seen now, nearly a decade later, the Heartbeat necklace feels like a particularly good example of what makes exceptional high jewelry endure. Scale alone is not enough. Nor is rarity. The strongest pieces tend to combine material value with narrative, allowing the wearer’s story to become part of the object itself.
With its 48-plus carats of rubies and diamonds, its vivid yellow center stone and its distinctly personal origin, the Firefly Diamond necklace succeeded on all three counts.
It was extravagant, certainly. But it was also intimate, which is what made it memorable.
