Page 119 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

M A L A C H I T E
The exploitation of malachite was extensive. The mineral is not only an important copper ore,
but it was widely used as a green pigment and as a coloring component in glazes and glass. In
addition, it occurs as a corrosion product on buried bronzes. Where the natural mineral was
locally available or obtainable by trade, malachite was carved into beads or used for inlay by
both Old and New World cultures. Etymologically, the word malachite is related either to the
Latin molochites, which was used by Pliny to describe a green jasper, or to the Greek malache
(mallow), because its color resembles that of the mallow leaf. PLATE 18 shows a good-quality
sample of the natural mineral.
Felice Fontana (1730-I805), the founder of toxicology, was the first to show that malachite
is a carbonate of copper (Fontana 1778). As a natural mineral, malachite can occur in quite
substantial deposits, often mixed with cuprite, azurite, or chrysocolla (copper silicate). Dana's
System of Mineralogy (Palache, Berman, and Frondel 1951) describes vast deposits of banded
malachite at the Demidoff copper mines in Siberia. During the early lsoos, this ore was mined
and cut into slabs for tabletops and large decorative pieces, such as the huge ornamental vases
that adorn the Winter Palace, former home of the Russian czars in St. Petersburg (formerly
Leningrad). Later, Fabergé used malachite for many of his exquisite objets de vertu (painted
eggs) (O'Neil 1971).
Georgeite is now recognized as an unstable isomer of malachite. It is a pale blue, amor­
phous, gel-like compound that was first identified by Bridge, Just, and Hey (1979) from a
copper mine in Western Australia. Georgeite was originally assigned a more complex
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chemical formula than malachite, with six waters of hydration, Cu5(C0 3 ) 3 (OH) 4 - H 2 0, until
Pollard, Thomas, and Williams (1991) synthesized it and clarified its composition, as described
in APPENDIX B, RECIPE 3.

TABLE 3.1 CHARACTERISTICS OF SOME BASIC CARBONATE MINERALS

MINERAL FORMULA CRYSTAL COLOR MOHS
NAME SYSTEM HARDNESS

malachite CuC0 3-Cu(OH) 2 monoclinic pale green 3.5-4
azurite 2CuC0 3-Cu(OH) 2 monoclinic vitreous blue 3.5-4
georgeite CuC0 3-Cu(OH) 2 monoclinic pale blue ?
chalconatronite Na 2 Cu(C0 3 ) 2 -3H 2 0 monoclinic greenish blue 3 - 4
rosasite (Cu,Zn) 2 C0 3 (OH) 2 monoclinic bluish green 4.5
aurichalcite (Cu,Zn) 5 (C0 3 ) 2 (OH) 6 orthorhombic pearly pale green 1-2
claraite (Cu,Zn) 3 (CO 3 ) (OH) 4 - 4H 2 O hexagonal translucent blue 2

C H A P T E R T H R E E
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