Studied geology and mining. Toured America under the patronage of Gustav III of Sweden (1783-84), carrying letters of introduction from Franklin. Published a report on mining in America (1783) and an account of his travels in the United States (1784).
Foreign member of the American Philosophical Society. Later became an expert on the geography and mineralogy of northern Europe.
Son Carl H. and Hedvig Ulrika (Benzelstierna) Hermelin. Married Maria Elisabet Sandels in 1773. Married Hedvig Augusta af Söderling in 1785.