appearance Dendritic tufa - branching structures that look similar to small shrubs Thinolitic tufa - large well-formed crystals of several centimeters These tufa types vary interchangeably both between individual tufa towers but also within individual tufa towers. There can be multiple transitions between tufa morphologies within a single tufa tower. Through time, many hypotheses were developed regarding the formation of the large thinolite crystals (also referred to as glendonite) in thinolitic tufa. It was relatively clear that the thinolites represented a calcite pseudomorph after some unknown original crystal. However, the original crystal was only determined when the mineral ikaite was discovered in 1963. Ikaite, or hexahydrated CaCO3, is metastable and only crystallizes at near-freezing temperatures. It is also believed that calcite crystallization inhibitors such as phosphate, magnesium, and organic carbon may aid in the stabilization of ikaite. When heated, ikaite breaks down and becomes replaced by smaller crystals of calcite. In the Ikka Fjord of Greenland, ikaite was also observed to grow in columns similar to the tufa towers of Mono Lake. This has led scientists to believe that thinolitic tufa is an indicator of past climates in Mono Lake because they reflect very cold temperatures. Tufa chemistry Rusell (1883) studied the chemical composition of the different tufa types in Lake Lahontan, a large Pleistocene system of multiple lakes in California, Nevada, and Oregon. Not surprisingly, it was found that the tufas consisted primarily of CaO and CO2. However, they also contain minor constituents of MgO (~2 wt%), Fe/Al-oxides (.25-1.29 wt%), and PO5 (0.3 wt%). Carbon and oxygen isotopes Carbon and oxygen isotopic compositions of Mono Lake tufas have the potential to reveal many interesting things about how water bodies mix in Mono Lake, how the climate changed throughout time in the Mono Basin, and how biology may or may not play a role in tufa formation. Steps have been made to understand the isotopic compositions of "modern" tufa and water isotopic composition in Mono Lake. Mono lake water DIC has a δ13C composition of 2 ‰ (relative to PDB), and a δ18O of -0.1 ‰ (relative to SMOW). Surrounding rivers feeding into Mono Lake have a δ18O of -14 to -17.5 ‰ and contains DIC with a δ13C composition of -14 ‰ . We observe that both the δ13C and δ18O compositions of Mono Lake are enriched compared to surrounding water. One explanation for the enrichment of δ18O in