Rare salt formations return to Great Salt Lake’s shores; take a tour while they last

Park rangers will lead groups to see the mirabilite mounds on Jan. 23 and 24.

(Photo courtesy of Utah State Parks) Rare mirabilite mounds have returned to the Great Salt Lake, and the public is invited to tour them Jan. 23 and 24.

The rare salt formations discovered on the shores of the Great Salt Lake in 2019 have returned, and officials at Great Salt Lake State Park are leading tours for people who want to see them up close. The mounds only form during the winter months, and they can grow to be several feet tall.

The formations aren’t made of table salt, so don’t try to lick them. Instead, the mounds are made up of Glauber’s salt, or “mirabilite.” The chemicals that make up table salt are sodium and chloride, while mirabilite is comprised of sodium, sulfate and water. If someone did eat mirabilite, they would have a rather unpleasant time — the mineral functions as a laxative, according to Utah Geology Survey geologist Mark Milligan.

Milligan said mirabilite itself is a fairly common mineral, but mounds like those found at the Great Salt Lake are unusual. Other mounds have been discovered around the world in Antarctica and Spain. He said there might be more in other places that haven’t been found yet.

Elliot Jagniecki, another geologist with UGS, explained that the mounds require very specific conditions to form. Underground springs in the south arm of the Great Salt Lake are rich in sodium sulfate. When that water is pushed up to the surface, contact with the cold air causes it to stabilize as mirabilite. As the spring water is pushed up, the crystals build up and form the mounds.

When temperatures rise to about 50 degrees Fahrenheit, the crystals become dehydrated, turn into a white, powdery mineral called thenardite, and fall apart. Thenardite is also made of sodium and sulfate but has fewer water molecules, said Jagniecki, adding that the crystals can survive at higher temperatures if they are kept hydrated. A mirabilite crystal in a plastic bag with a sponge, for example, will stay stable until about 90 degrees.

But don’t take any of the Great Salt Lake crystals. Research is being conducted on the mounds before they dissolve in the spring, so Great Salt Lake State Park officials are asking members of the public not to damage or remove parts of them.

(Photo courtesy of Utah State Parks) People who come to tour the mounds should remember waterproof shoes and a mask.

Tours of the salt mounds will be available Jan. 23 and 24, every half-hour from 11 a.m. to 4 p.m. People who want to attend must book a slot in advance online. The tour costs $3 per person in addition to a $5 fee for vehicles entering the park.

People who want to go see the mounds should wear waterproof shoes for the tour. Masks will be required.