The Geology of Tin: Cassiterite, Concentrated by Its Own Weight
Tin's main ore, cassiterite, is dense enough to concentrate by simple gravity sorting in riverbeds, the same physical principle behind gold placer deposits.
Tin’s main ore mineral, cassiterite (tin oxide), shares a real physical property with gold, covered on gold’s own geology page: it is dense enough to resist being washed away with lighter sediment, which is why alluvial placer deposits are such an important tin source alongside hard-rock mining.
Hard-rock and placer sources, both real
Cassiterite forms primarily in granite-related hydrothermal veins and pegmatites, similar in setting to some of the lithium and tungsten deposits covered on their own geology pages. Where that primary rock has weathered and eroded, cassiterite’s high density (nearly 7 g/cm³) lets it concentrate in riverbeds and, in Indonesia’s case, offshore marine placer deposits, dredged directly from the seabed.
Why DR Congo appears here too
DR Congo’s tin production, alongside the cobalt and copper covered on their own pages, reflects the same Central African geological province hosting multiple economically important metals together, a real, recurring pattern rather than coincidence.
Sources: cassiterite geology and deposit settings draw on standard economic geology references (USGS Mineral Commodity Summaries); production figures reference the production data elsewhere on this site.