While all actinides are radioactive, actinides and actinide compounds comprise a significant portion of the Earth's crust. There is enough thorium and uranium to be commercially mined, with thorium having a concentration in the Earth's crust about four times that of uranium. The global production of uranium in 2021 was over six million tons, with Australia having been the leading supplier. Thorium is extracted as a byproduct of titanium, zirconium, tin, and rare earths from monazite, from which thorium is often a waste product. Despite its greater abundance in the Earth's crust, the low demand for thorium in comparison to other metals extracted alongside thorium has led to a global surplus.