Black limestone shows dark color because of the organic material in the rock. Similar to shale, it does not take much organic carbon (a few percent) to turn the rock into black color.
Even this is a very fine grain rock, it can be identified as a limestone simply by its softness (softer than knife blade). Of course, acid test would further confirm it. The while band on this sample is a fracture in the rock filled by calcite deposit.
Some varieties of limestone perform well in these uses because they are strong, dense rocks with few pore spaces. These properties enable them to stand up well to abrasion and freeze-thaw. Although limestone does not perform as well in these uses as some of the harder silicate rocks, it is much easier to mine and does not exert the same level of wear on mining equipment, crushers, screens, and the beds of the vehicles that transport it.