Matter composed of strange quarks is thought to exist at the center of
some neutron stars, and in quark stars. Unlike neutronium, strange
quark matter is thought to be stable even outside of dense bodies, and
so there could be strange quark asteroids. Such asteroids would have
incredible density. Strange matter might have been formed in the Big
Bang itself.

Could a strange quark matter object strike and pass through the Earth
without destroying it? Some observational data suggests that two such
occurences might have occurred in 1993! Seismic events were found
where a distinct straight line signal was detected, the kind phenomena
thought to be produced by an object passing through the Earth at 40
times the speed of seismic waves. Entrance points and exit points were
calculated. Of course there is no proof that this was quark matter,
but scientists so far have no other explanation.

http://news.bbc.co.uk/1/hi/sci/tech/2502755.stm

Could strange quark matter be the dark matter that everyone is looking
for?

Double-A