Calcite forms at the water's surface where there is contact with air. Below the air domes in cenote Nohoch Nah Chich, vast dunes of calcite have built up from the calcite settling to the cave floor over thousands of years.
String of Pearls
Harry Gust started exploring String of Pearls in 2006. Exploration was interrupted when the landowner closed access to the cenote during land disputes. The cave is open for diving again, under arrangement.
New GUE sidemount class
The diver training agency Global Underwater Explorers has a cave sidemount class for advanced cave divers (prerequisite GUE C2).
Sac Actun on sidemount
Sidemount is a versatile diving configuration that can be used to travel through very small cave passages, where backmount configuration may not be passable.
In 2018 the Mexican underwater cave systems Sac Actun and Dos Ojos were connected. Dos Ojos was absorbed into the bigger system Sac Actun, making Sac Actun the world's longest underwater cave system.