Page 165 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

TABLE 5.1 CHARACTERISTICS OF SOME BASIC COPPER SULFATE MINERALS

MINERAL FORMULA CRYSTAL COLOR MOHS
NAME SYSTEM HARDNESS

chalcanthite CuS0 4 -5H 2 0 triclinic deep blue 2 - 4
brochantite Cu 4 S0 4 (OH) 6 monoclinic vitreous green 2.5-4
antlerite Cu 3 S0 4 (OH) 4 orthorhombic vitreous green 3.5
posnjakite Cu 4 S0 4 (OH) 6 -H 3 0 monoclinic vitreous green 2-3
bonatite CuS0 4 -3H 2 0 monoclinic pale blue 2-3
Strandberg's Cu 2 . 5 (OH) 3 S0 4 -2H 2 0 monoclinic pale green ?
compound
langite Cu 4 (S0 4 )(OH) 6 -2H 2 0 monoclinic greenish blue 2.5-3
Tutton's salt Cu(NH 4 ,S0 4 ) 2 -6H 2 0
schulenbergite (Cu,Zn) 7 (SO 4 ,CO 3 ) 2 (OH) 10 .3H 2 O rhombohedral pearly light 2
greenish blue
synthetic Pb 4 Cu(C0 3 )(S0 4 )
compound
caledonite Cu 2 Pb 5 (S0 4 ) 3 C0 3 (OH) 6 orthorhombic resinous green/ 2.5-3
bluish green
beaverite Pb (FeCuAl) 3 (S0 4 ) 2 (OH) 6 rhombohedral blue green ?
spangolite Cu 6 Al(S0 4 )Cl(OH) 12 -3H 2 0 hexagonal bluish green 2
guildite CuFe(S0 4 ) 2 (OH)-4H 2 0 monoclinic yellow brown 2.5
devilline CaCu 4 (S0 4 ) 2 (OH) 6 .3H 2 0 monoclinic pearly green 2.5
ammonium copper Cu(NH 4) S0 4 ) 2 -2H 2 0
sulfate hydrate

identification of a basic copper (II) sulfate as a patina constituent on bronzes from Bourbon-
l'Archambault in central France. This is the first reference in the literature to a basic sulfate com­
pound in this context; during the late nineteenth and early twentieth centuries, difficulties in
the identification of these various compounds often resulted in all of them being referred to as
"brochantite."
Brochantite is a vitreous green, monoclinic mineral with a Mohs hardness of 2.5-4, first
identified from the Bank mines of Sverdlovsk, Ekaterinburg, in the Ural Mountains of Russia.
A melt-mount preparation is shown in PLATE 34.
Antlerite is a vitreous green, orthorhombic mineral with a Mohs hardness of 3.5; it is named
after the Antler mine in Mohave County, Arizona. Vernon (1933) appears to be the first to

C H A P T E R F I V E
148