Acid fracturing is a promising technique to stimulate the induced unpropped (IU) fractures which are created in shales during hydraulic fracturing. These fractures have enormous surface area, but close during production due to their inability to accommodate proppants. The use of acid has been proposed as a way to keep these IU fractures open after pumping has ceased. A successful acid fracturing treatment requires the acid to effectively etch the shale fracture surfaces to create a connected flow pathway that will remain open when stress is applied. This requires the acid etching to be non-uniform. Changes in fracture surface topography and mechanical properties are critical in determining how the fracture conductivity will change with stress. In this study, 55 preserved shale samples from Barnett, Eagle Ford, Haynesville and Utica shale covering a wide range of mineralogy (with clay 3.4 - 75.6 wt% and carbonate 1.9 - 83.7 wt%) were used to systematically investigate the effect of acid treatment on their fracture surface topography, mechanical properties and fracture conductivities. The mechanical properties of the fracture surface were measured using indentation tests. Fracture conductivities were computed with a numerical model that simulates unpropped fracture closure. The results showed that the roughness of all the fracture samples increased after acid etching, but to different extents. The roughness was initially 1.58 ± 0.29 µm and developed into two groups: the low roughness group for roughness within 6 µm, and the high roughness group with roughness over 10 µm and up to 43.71 µm. Although carbonate-rich samples were more likely to produce high roughness, high carbonate content did not necessarily always lead to rougher surfaces. The amount and the distribution pattern of carbonate minerals affected the etched surface topography. On surfaces of low etched roughness, isolated pits with diameter of 10-30 um were formed, while profile valleys at millimeter scale were developed on surfaces of high roughness, and some of these valleys were connected to form channels. Acid caused additional shale softening than brine exposure, mainly by removal of carbonate minerals. Acid fracturing was found to improve fracture conductivities under reservoir pressure mostly in cases of high etched roughness; while fractures with low etched roughness, conductivities were lower than or close to factures treated by brine. Experimental results on surface topography, mechanical properties and the modeled fracture conductivities of acid-fractured shales of a wide range of mineralogy are presented. The results are important in selecting candidate shale plays for acid fracturing, and also provide useful parameters for modeling and field design.