Nuclearites are hypothetical objects consisting of nuggets of strange quark matter or a strangelet surrounded by an electron shell, forming an atom -like neutral system, but with masses much larger than a normal atom. These heavy compact particles were first proposed by E. Witten, and the name coined by A. De Rujula and S. L. Glasgow to describe such particles colliding with the Earth's atmosphere, by analogy to more conventional meteorites. It is predicted that nuclearites would travel at hundreds of kilometers per second. Owing to their high energies and mass to size ratio, they should form streaks of light in the lower atmospheric regions. To date, no nuclearites have been successfully observed, but this failure itself places constraints on some theories of dark matter.