By the second quarter of the 18th century, a number of private coal pits were operating on a commercial scale in coalfield located the area we now know as Midlothian.  Miners immigrated to Chesterfield from Wales, England and Scotland.  The Wooldridge family from East Lothian and West Lothian in Scotland was among the first to undertake coal mining in the area.  It is likely that the mining community was eventually named after their Mid-Lothian Mining enterprise, a combination of their two home town names.  The Heths, beginning with Colonel Henry "Harry" Heth (died 1821), who emigrated about 1759, who were English investors, opened coal pits in the county.

According to records held by the Library of Virginia, on January 25, 1832, Beverley Randolph, John Heth, and his younger brother, Beverley Heth (1807 1842) petitioned the Virginia General Assembly for the first coal mining corporation to be chartered in Virginia.  After substantial opposition to the concept, this was accomplished the following year with the incorporation of the Black Heath Colliery.

Coal mining at Black Heath was both difficult and dangerous work, and there were fatal explosions.  On March 18, 1839, 40 men, mostly African American slaves, were killed in a 700 foot shaft at the Black Heath mine.  On June 15, 1844, a mining explosion at Black Heath killed 11 more men.  After the second incident, the mine was closed until 1938.

Source: Wikipedia