Pure penfieldite is colorless, however, due to lattice defects or foreign admixtures, it can be white, yellow or even blue.

[2] After it is dissolved in water, penfieldite leaves a lead oxychloride residue behind that is yellowish white in color.

[1] In both the 8th and the 9th edition of the Strunz Mineralogical tables, penfieldite is classified as belonging to the oxyhalides (and related to double halides).

The Dana classification also assigns penfieldite to the oxyhalides, but classifies it according to chemical composition in the subdivision "Oxihalides and hydroxyhalides with the formula A2(O,OH)Xq".

[2] It is the alteration product of a lead-bearing slag contacting seawater in Greece and Italy, and in Chile, it can be found in an oxidized hydrothermal lead deposit.