Erythrite and pharmacolite are common associated minerals. Secondary weathering incrustations of erythrite, hydrated cobalt arsenate, are common. Examples of arsenate-containing minerals include adamite, alarsite, annabergite, erythrite and legrandite. At San Juan, Chile, it is associated with erythrite, cuprite, malachite and cobaltian wad. It alters to the arsenate erythrite in the secondary environment. About two weeks after McKinley and Darragh, LaRose noticed erythrite along the tracks. Erythrite crystallizes in the monoclinic system and forms prismatic crystals.