Sydney Hobart Ball (1877-1949) was an American mining geologist and engineer. Born in Chicago, he studied geological engineering at the University of Wisconsin, completing his A.B. in 1901 and his Ph.D. in 1910. From 1903 to 1906 Ball participated in the Southwestern United States Geological Survey, and was responsible for mapping 8,550 square miles of southern Nevada and southeastern California. In 1907 he became technical head of a prospecting expedition undertaken by the Société internationale forestière et minière du Congo (Forminière), a company jointly established by Leopold II of Belgium and the American Ryan-Guggenheim group to extract mineral and agricultural resources from the Kasai region of the Congo. Working with several American mining engineers, including Millard K. Shaler, Ball discovered gold, copper, tin, iron, bauxite, oil shale and diamond deposits in Kasai. His expedition led to the creation of the Belgian Congo-Angolan diamond fields, one of the largest diamond mining operations in Africa.

For his work Ball received the Chevalier of the Royal Order of the Lion from the Belgian king Albert I, and was appointed consulting geologist to Forminière (1909). Ball worked for Forminière from New York. In 1917 he joined Allen Hastings Rogers and Lucius Mayer in the mining consulting firm Rogers, Mayer and Ball. He engaged in mining expeditions around the globe for Rogers, Mayer and Ball and in private practice from the 'teens to the 1940s, travelling to Canada, Mexico, Cuba, Haiti, Venezuela, Peru, Chile, Greenland, Russia, Japan, Portugal and across the United States.

Ball was a prominent figure in the diamond and jewelry industry in the United States. He was a key member of the Jewelers Publicity Committee of the American National Retail Jewelers' Association and the Gemological Institute of America. He also held leadership positions in associations for geologists and mining engineers, such as the Society of Economic Geologists, the American Institute of Mining and Metallurgical Engineers and the Mining and Metallurgical Society of America. Ball's research was published in many prominent journals on geology. From 1927 to his death he also wrote annual reviews of the diamond industry for professional journals such as the Jewelers Circular, and from 1934 published an annual chapter on gem stones in the United States Bureau of Mines Minerals Yearbook.

Also figuring notably in the papers are the following members of Sydney Hobart Ball's family:

Farlin Quigley Ball (1838-1917), Ball's father, was a native of Shelby County, Ohio. After the Civil War he settled in Chicago, where he held a number of significant judicial offices, and served as judge on the Superior Court of Cook County. In 1868 he married Elizabeth Hall (1842-1940), with whom he had two children who survived infancy. Sydney's brother, Farlin Herbert Ball, graduated from the University of Chicago Law School in 1897 and became Circuit Court judge for Cook County in 1920.

Mary Ainslie Ball (1880-1945), Ball's wife, was born in Denver, Colorado. She wed Sydney in 1913 and lived with him in New York for most of their marriage. Katherine Ball (1916-1935), Sydney and Mary's first child, was born in New York City. She attended Choate Rosemary Hall boarding school and died while studying at Smith College in Massachusetts. Mary Virginia Ball Moister (1918-2010), the younger child of Sydney and Mary, was born in New York. Called Virginia or Ginnie, she attended Choate and Smith, studied physiology at Laval University (1944-1949), and graduated from Harvard Medical School in 1956. She later practiced medicine at the Dartmouth-Hitchcock Medical Center in Lebanon, New Hampshire. In 1961 she married Frank Corbin Moister.