Copper(I) iodide is white, but samples often appear tan or even, when found in nature as rare mineral marshite, reddish brown, but such color is due to the presence of impurities.

It is common for samples of iodide-containing compounds to become discolored due to the facile aerobic oxidation of the iodide anion to molecular iodine.

The ions are tetrahedrally coordinated when in the zinc blende or the wurtzite structure, with a Cu-I distance of 2.338 Å.

[4] Copper(I) iodide reacts with mercury vapors to form brown copper(I) tetraiodomercurate(II): This reaction can be used for the detection of mercury since the white CuI to brown Cu2[HgI4] color change is dramatic.

[14] In combination with 1,2- or 1,3-diamine ligands, CuI catalyzes the conversion of aryl, heteroaryl, and vinyl bromides into the corresponding iodides.

[citation needed] CuI is used as a source of dietary iodine in table salt and animal feed.