  Stable lumps of quark matter may be present in cosmic rays at a flux level,
which can be detected by high precision cosmic ray experiments sensitive to
anomalous "nuclei" with high mass-to-charge ratio. The properties of these
lumps, called strangelets, are described, and so is the production and
propagation of strangelets in cosmic rays. Two experiments underway which are
sensitive to a strangelet flux in the predicted range are briefly described.
Finally it is summarized how strangelets circumvent the acceleration problem
encountered by conventional candidates for ultra-high energy cosmic rays and
move the Greisen-Zatsepin-Kuzmin cutoff to energies well above the observed
maximum energies.
