Yes: stone.

Granite flooring, to be specific.

It seems that the material most commonly associated with kitchen countertops, tile, and the facades of old churches has found its way into private jets.

Traditionally, flooring on Gulfstream's and other private jets has been carpet and, in some cases, wood.

But the trend these days is custom stone veneers.

For Gulfstream, the ultra-thin granite veneers are imported and installed in the aircraft's galley and bathrooms at one of the company's finishing facilities around the US.

Stone is just the latest addition to the designer's arsenal of offerings, needed to meet the needs of the company's highly discerning customers.

"Depending on the client, it can take as much as three to four months to define an interior," Crow said. "They have an intense of focus on the details. As far as interior options go, Gulfstream's customers tend to lean towards natural-looking materials."

"People want an environment that's calming and serene," Crow added. "So it's not really the place to do high contrast."

Gulfstream launched the stone-flooring option for its new G600 jet last November at the National Business Aviation Association show in Las Vegas. The G600 can seat up to 19 passengers with a range of more than 7,000 miles and can operate as high as 51,000 feet.

The G600 is expected to enter service in 2019 and will have a price tag of $54.5 million.