In the inverse order of evaporite deposition, which mineral is deposited last?

• A. Anhydrite
• B. Calcite
• C. Halite
• D. Sylvite

Answer: (A)

As evaporites form, minerals precipitate in a specific sequence as the brine becomes more concentrated; the more stable a mineral is at high salinity, the later it appears. When we talk about the inverse order, we’re reversing that progression.

Anhydrite is tied to the very evolved, highly saline conditions that develop late in the evaporation process. It forms from gypsum under hotter, drier conditions and higher salinity, so in the reversed (inverse) sequence it occupies the final position. That contrast with minerals like calcite, which precipitate earlier, helps place anhydrite at the end of the inverted order.