Strangelets are theorized cosmological objects composed of an exotic form of matter known as strange matter or quark matter. This form of matter is created in the cores of particularly massively neutron stars. In neutron stars, the remnants of collapsed stars with masses between 4 and 8 times that of our sun, pressure and temperature is so intense that the protons and electrons in atomic nuclei fuse to become neutrons. The resultant matter is sometimes referred to as neutronium, a sea of neutrons packed far more densely than conventional matter.
Sometimes the pressure and gravity in the centres of neutron stars is so massive that the neutronium collapses into its constituent particles, quarks. This results in agglomerations of so-called strange quarks bound to each other directly much in the same manner that the transition from conventional star to neutron star results in seas of neutrons bound directly together. The names physicists have given this type of matter are "quark matter" or "strange matter". This may be regarded as a phase change, like changing from a liquid to a solid, only at densities many orders of magnitude greater than those occurring in this solar system.
It has been hypothesized that strangelets (sub-stellar agglomerations of strange matter) may be able to exist independently from the quark stars which created them. If so, there may be many strangelets in this universe, a possible explanation for the dark matter problem. Since strangelets maintain such deep gravity wells for objects of their size, calculations show that strangelets coming in contact with ordinary matter would overwhelm this matter with their gravitational fields, breaking down the ordinary matter into strange matter. If strangelets exist and keep coming into contact with ordinary matter indefinitely, it may be only a matter of time (albeit a cosmologically long duration of time) before strangelets swallow all the conventional matter in the universe.
Though the existence of strangelets has not yet been proven conclusively, there exist observed stars too dense to be conventional neutron stars yet too sparse to be black holes (i.e., they possess volume). Also, strangelets have been blamed for unexplained seismic events. If a small strangelet penetrated the Earth at relativistic speeds, it would indeed perturb ordinary matter, though to exactly what degree has not yet been established in a consensus among the physics community. Similar to the neutrino before its detection in 1956, the strangelet remains a theoretical construct until we develop instruments fine enough to either verify or disprove their existence.