Mg ii absorbers induce reddening on background quasars .
We measure this effect and infer the cosmic density of dust residing in these systems to be \Omega \approx 2 \times 10 ^ { -6 } , in units of the critical density of the universe , which is comparable to the amount of dust found in galactic disks or about half the amount inferred to exist outside galaxies .
We also estimate the neutral hydrogen abundance in Mg ii clouds to be \Omega \approx 1.5 \times 10 ^ { -4 } , which is approximately 5 % of hydrogen in stars in galaxies .
This implies a dust-to-gas mass ratio for Mg ii clouds of about 1 / 100 , which is similar to the value for normal galaxies .
This would support the hypothesis of the outflow origin of Mg ii clouds , which are intrinsically devoid of stars and hence have no sources of dust .
Considerations of the dust abundance imply that the presence of Mg ii absorbers around galaxies lasts effectively for a few Gyr .
High redshift absorbers allow us to measure the rest-frame extinction curve to 900 { \AA } , at which the absorption by the Lyman edge dominates over scattering by dust in the extinction opacity .