When volcanic ash chemically reacts with lake salts, what is formed?

• A. Halite
• B. Natural zeolites
• C. Calcite
• D. Gypsum

Answer: (A)

Saline lake waters concentrate the dissolved ions as evaporation removes water. The dominant ions in such a brine are sodium and chloride. When the solution becomes saturated with NaCl, it readily crystallizes as halite. The volcanic ash mainly affects surfaces and can influence nucleation, but the mineral that precipitates from a concentrated NaCl brine is halite, not a silicate or sulfate mineral.

Other minerals would require different chemical conditions: gypsum forms from calcium sulfate, calcite from carbonate-rich conditions, and natural zeolites form from specific reactions between ash and siliceous, often alkaline waters—conditions not given by simple evaporation of a lake brine.