[5][6] Carminite belongs to the orthorhombic crystal class (2/m 2/m 2/m) and has space group C ccm or C cc2.

[9] The structure consists of linked octahedra of iron surrounded by oxygen and hydroxyl which are aligned parallel to the c axis.

They also occur as acicular crystals, in spherical or tufted aggregates and as fibrous or drusy masses.

[10] For carminite the orientation is X = c, Y = a and Z = b[6][7] and the refractive indices are high, with nα = 2.070, nβ = 2.070, nγ = 2.080, only a little less than diamond at 2.4.

[10] Carminite is formed as an uncommon alteration product of arsenopyrite (FeAsS) in the oxidized zones of some lead-bearing deposits.

[4][5][6] Common associates are wulfenite, scorodite, plumbojarosite, mimetite, dussertite, cerussite, beudantite, bayldonite, arseniosiderite and anglesite.

[4][6] The type locality is the Louise Mine, Bürdenbach, Altenkirchen, Wied Iron Spar District, Westerwald, Rhineland-Palatinate, Germany[4] where it is associated with beudantite.

[4][7] At the Hingston Down Consols mine in Cornwall, England, carminite occurs with scorodite, mimetite and pharmacosiderite.

[7] The ores of the Ojuela Mine, Mexico, are replacement deposits in limestone and consist of galena, sphalerite, pyrite, and arsenopyrite in a matrix of quartz, dolomite and fluorite.

On a dump near the north shaft blocks of massive scorodite containing seams and pockets of arseniosiderite and small areas of dussertite and carminite have been found.