What is the primary composition of hallite?

Hallite is primarily composed of rock salt, which is the mineral form of sodium chloride (NaCl). This mineral is typically found in sedimentary layers and forms through the evaporation of seawater or salt lakes, resulting in large deposits. The term "hallite" specifically refers to this mineral, emphasizing its crustaceous and crystalline structure. This connection to rock salt distinguishes it as a unique geological formation, primarily associated with locations where ancient bodies of water have evaporated over time, leading to the accumulation of salt deposits.

In contrast, granite is an igneous rock formed from the slow crystallization of magma beneath the Earth's surface, marble is a metamorphic rock derived from limestone, and silt is a fine-grained soil material. These other options do not pertain to the characteristics of hallite, further reinforcing the correctness of identifying rock salt as its primary composition.