What is the inert material used in construction that is composed of calcium sulfate dihydrate?

Gypsum is the correct choice as it is a natural mineral composed of calcium sulfate dihydrate, which is commonly used in construction, particularly in the form of drywall or plaster. Its properties make it an excellent building material because it is fire-resistant, can help with sound insulation, and is easy to work with. Gypsum's ability to add structural stability and its non-combustibility make it a preferred choice in various applications, especially in walls and ceilings.

In contrast, vinyl is a synthetic material often used for flooring and siding but does not contain calcium sulfate. Wood is an organic material used for framing and various structural elements but lacks the chemical composition of gypsum. Concrete, while a versatile and widely-used construction material made from a mixture of cement, sand, gravel, and water, does not contain calcium sulfate dihydrate either. Thus, gypsum is distinguished by its specific mineralogical composition and its unique properties that benefit building construction.