It's a simple test: When you first behold the beach, do you say "Wow"? Once more, Ron Hall assiduously gathers evidence among the grains, this time searching for the chemistry of the perfect ten

This story originally appeared in Condé Nast Traveler's November 1996 issue.

In the four previous installments of Great Beaches of the World, my selection process has relied heavily on the Wow Factor. If on first setting eyes on a beach I emitted an involuntary "Wow!" then I included it in the list; otherwise, I left it out. What could be more objective than that?

But faced with the multitudinous choice and infinite gradations of Caribbean beaches, I felt that the Wow Factor needed to be backed up with something a little more scientific. Accordingly, as I write, my desk is adorned with rows of meticulously labeled piles of sand, systematically scooped up from just above the high-water mark of each beach I visited. As a result, I feel equipped to pronounce on some hotly contested issues. . . such as which Caribbean islands have the whitest beaches and which beaches have the finest sand.

In reality, of course, there is no such thing as a pure white beach, whatever the brochures might say. The whitest I have found anywhere in the world was on the Mediterranean island of Lipari, but this turned out to be a man-made imposter. The beach had for years been used as a dump for spoil from a neighboring pumice quarry—hence its unreal, and not very attractive, snowy-white appearance.

The rich, creamy-white beaches that are the trademark of the Caribbean islands are usually a mix of two kinds of sand: the ivory-colored calcareous variety (the broken-down skeletal remains of dead corals) and black, brown, or gray detrital sand (the result of the weathering of the island's rock). Grains of detrital sand can add subtlety and interest to the color of a coral beach, like dots on a pointillist painting, but of course the more of it there is, the less white the overall effect will be.

Of the collection of sand samples on my desk, three beam out as having the whitest ingredients.

The first is from the cluster of uninhabited islets confusingly known as the Tobago Cays (part of the Grenadines, and nothing to do with Tobago). Each morning, an armada of yachts and excursion boats anchors there so that their occupants can spend the day feasting on the colors of sand, reef, and sea—exceptional even by Caribbean standards. So intense is the upward glow from the sea that the circling gulls appear to have bright turquoise underbellies, an effect that seems to create a strange new species. My sand sample from the Tobago Cays is of powdery coral spiked with minute gray dots of granite, the consistency of finely ground pepper.

My second exhibit is from the even tinier Grenadines islet of Mopion—an isolated sand shoal just a four-minute speedboat ride from the private resort island of Petit St. Vincent. Hazen Richardson, the flamboyant owner of PSV, has adopted Mopion, renamed it immodestly after himself (Petit St. Richardson), and erected a single thatched umbrella on its central point, making it look just like the castaway island of a million comic strips. His guests on PSV take turns being speedboated off to Mopion and left there (with a well-stocked hamper) for an hour or two of Crusoic fantasy. The sand is a micron or so coarser than that of the Tobago Cays, but it is an even more homogeneous creamy white.