International manganese samples in this collection were acquired from various countries, typically by geoscientists and university professors of the corresponding region. Manganese samples from the United States were collected in the field primarily by other USGS scientists noted in the dataset. The dataset corresponds to Hewett's physical collection of manganese-bearing samples re-established in 2023-2024 under the National Geological and Geophysical Data Preservation Program. Individual samples were assigned a new USGS Sample ID once the sample locality was identified. Each new sample number has an assigned cabinet letter and drawer number so that users can readily locate physical samples in the reorganized collection. The dataset includes location (state and site-specific names such as mines, claim(s), prospects, and deposit groups), latitude and longitude, origin of coordinates, sample type, collector of sample (if given), mineral name (if given), qualitative volume estimates for manganese oxide in each sample, and mass of samples in kilograms and grams. It is important to note that one mine, claim, or prospect can have multiple samples with different USGS identification numbers. This collection of manganese samples was assembled by Donnel Foster Hewett (1881-1971), an economic geologist and mineralogist with the USGS for fifty-nine years, serving for a period of time as Chief of the USGS's Metalliferous Geology Section. His study of manganese deposits aided in wartime steel production and earned him the nickname, "Mr. Manganese.” He is credited with the discovery of two major economic deposits, including the Minas Ragra mine, a major vanadium producer in the Pasco Region of Peru. Throughout the first half of the 20th century, Hewett provided an overall deeper understanding of metalliferous ore genesis in various geological settings.