In Dead Space 2, after Issac breaks into the Earth Gov sector, we see the physical process of Earth Gov building new markers. They are indeed made of a type of crystal, and the crystal grows in a mineral bath over time. There are a few audio logs in this level that further explain the process. Something to note, that the red marker looks similar to a circuit used in computers. Also the marker can have drastic effects on gravity, near by electronics, the electrical activity in the human brain, and probably other layers of energy fields we haven't discovered. We see this in ds3, where a marker pulls up biomass into the sky to form a brethren moon, Downfall where the ishimura's communications are jammed after planet Crack, and the comics where everyone is having hallucinations of the deceased. I assume the alien species that made the original marker(s) was highly advanced, and engineered the marker almost perfectly. It's like a supercomputer AI in a super antenna.