Lake Lucero in White Sands National Monument

Many people visit White Sands National Monument, but to see firsthand where the white sand comes from you need to plan ahead to get on a Lake Lucero Tour.
These sparkling gypsum crystals (called selenite) are the source of sand that forms the dunes of White Sands National Monument.

My parents and I planned our trip so we would visit during one of the times the reservation-only Lake Lucero Tours are offered. You can only go here on a tour.

Those mountains provided the source of the gypsum.

Water (rain) dissolves gypsum in the surrounding mountains and carries it down to the basin where it gets concentrated. As water evaporates the crystals form. The white sands are the broken up crystals that have been blown by the wind, which form the largest gypsum dunefeld in the world.

The white sands in a wind-swept dune after the particles have been broken up.

The large crystals formed thousands of years ago when a lake the size of Rhode Island filled this basin. It’s fun to imagine that these crystals formed when this place was much wetter and lush and there were mammoths, camels, and saber-tooth tigers roaming about leaving behind footprints that can be seen today.

But crystal formation is also an ongoing process that has been going on for thousands of years. Water that flows down into the playa is still saturated with more gypsum and more crystals form beneath the ground or during monsoon season. Though the crystals that form today tend to be smaller than the ancient crystals.

It didn’t feel right to me that we could freely walk across the crystals and feel them crunching beneath our feet. But the ranger assured us that it’s OK because they just erode away very quickly anyway and they are constantly being exposed due to erosion. Still, we were told not to collect any crystals.

What surprised me the most was that the crystals are made out of the same material as crystals in Mammoth Cave National Park in Kentucky (which is where I spent last summer). Both are gypsum, which is also what makes up drywall. They differ in shape and the crystals are called different things (selenite at White Sands, gypsum flowers at Mammoth Cave) so I think there must be something else different about them (any geologists out there?).

Gypsum flowers in Mammoth Cave (photo from last summer)

Gypsum (selenite) at White Sands. It is amber in color due to organic matter, but turns white as it weathers.

Because of what I'd learned at Mammoth Cave, I was surprised to see gypsum at all on the surface. It is a mineral that dissolves easily in water. At Mammoth Cave, the Woodland people would collect gypsum from the cave. We don’t know how they used it because when they brought it out to the surface, it dissolved and got carried away by the rain and didn’t leave traces behind. 

But in New Mexico, with the now arid climate, gypsum exists on the surface because it pools in the basin and also there is limited rain so we get to see the crystals on the surface before they get eroded into sand or dissolved. How cool that the conditions are “just right” for this to happen.

So much sparkle

The environments at Mammoth Cave and White Sands are strikingly different— a dry, dark cave in Kentucky and the extreme brightness of southern New Mexico. But the shimmering amazing sparkle of the crystals in both places evokes a similar sense of awe. Like being transported to glitter-filled world.

More Information

Get tickets by phone or on recreation.gov one month in advance. Apparently the April or November tours have better chances that there will be water in the lake so tend to have more birds, butterflies, and flowers than we saw in December.

Don't forget to stop by the visitor center to do their Junior Ranger program.