___________ is rough, irregular stone that is used as fill to provide a rustic appearance.

Rubble is indeed the correct answer because it refers to rough, irregular stones that are often used in construction for various purposes, including as fill in landscaping or building projects. Its natural, unrefined appearance makes it popular for achieving a rustic aesthetic in both residential and commercial settings. Rubble can provide structural benefits as well as an appealing texture, making it suitable for various applications where a more organic look is desired.

Granite is a hard, crystalline rock typically used for countertops, flooring, and other polished surface applications rather than for a rustic fill. Limestone, while used in construction, is more often associated with building stones or crushed for cement and does not typically convey the same rustic appearance as rubble. Slate, on the other hand, is a fine-grained metamorphic rock commonly used for roofing and flooring, noted for its smooth surfaces but not for a rough, rustic fill. Thus, rubble stands out as the appropriate choice in this context.