Azurite and Malachite

© Blackwell Science Ltd, Geology Today, Vol. 17, No. 4, July–August 2001152

Minerals explained 33Azurite and malachite

faunas of the oceanic and marginal environments ofthe Iapetus Ocean were an integral part of the Ordo-vician radiation events, whereas the Oslo Basin, mar-ginal to the developing Caledonides, provided anearly Silurian refuge for some Ordovician taxathrough the end Ordovician extinctions. ORS molassebasins associated with the deforming and risingCaledonides contain many significant terrestrial fos-sils marking the early stages of the evolution of life onland.

Suggestions for further readingThis section includes a number of review articles andsymposia on the uses of fossils in the study of moun-tain belts together with a few articles on palaeonto-logical studies in the Scandinavian Caledonides.Rudolf Trümpy’s address to the Geological Society in1971 contains the classic and often repeated quota-tion, ‘One bad fossil is worth a good working hypoth-esis’.Bruton, D.L. & Harper, D.A.T. 1981. Brachiopods and

trilobites of the early Ordovician serpentine OttaConglomerate, south-central Norway, NorskGeologisk Tidsskrift, v.61, pp.153–181.

Bruton, D.L. & Harper, D.A.T. 1988. Arenig –Llandovery stratigraphy and faunas across theScandinavian Caledonides. In The Caledonian – Ap-palachian Orogen (ed. A. L. Harris & D. J. Fettes),Geological Society Special Publication, v.38, pp.247–268.

Bruton, D.L. & Harper, D.A.T., eds. 1992. Fossils fromfold belts, Terra Nova, v.4, pp.178–253.

Cocks, L.R.M. & Fortey, R.A. 1982. Faunal evidencefor oceanic separations in the Palaeozoic of Brit-ain, Journal of the Geological Society, v.139, pp.465–478.

Darwin, C. 1839. Journal of Researches into the Geologyand Natural History of the Various Countries visited byH.M.S. Beagle, under the Command of Captain FitzroyR.N. from 1832–1836. Henry Colburn, London.

Fortey, R.A. & Cocks, L.R.M. 1990. Fossils and tec-tonics. In: Palaeobiology: a Synthesis (eds D. E. G.Briggs & P. R. Crowther), pp.482–490.Blackwells, Oxford.

Fortey, R.A. & Cocks, L.R.M. (conveners). 1986. Fos-sils and tectonics, Journal of the Geological Society,v.143, pp.149–220.

Harper, D.A.T. 1998. Interpreting orogenic belts:principles and examples. In: Unlocking the Strati-graphical Record (eds P. Doyle & M. R. Bennett),pp.491–524. John Wiley and Sons, Chichester.

Hughes, N.C. 1999. Statistical and imaging methodsapplied to deformed fossils. In: NumericalPalaeobiology (ed. D. A. T. Harper), pp.127–155.John Wiley and Sons, Chichester.

Lyell, C. 1830–1833. Principles of Geology, Vol. 1.John Murray, London.

Trümpy, R. 1971. Stratigraphy in mountain belts,Quarterly Journal of the Geological Society, v.126,pp.293–318.

Both azurite and malachite are well known, to minersand mineralogists alike, for their outstanding beautyof colour, blue and green, respectively – in the case ofazurite, not only for the beauty of its colour but alsofor its striking crystallizations and, of malachite, forits colour and aesthetic qualities as a decorativemedium. Together, they account for most of the blueand green stains associated with a weathering copperdeposit, however lean it may be in copper values.Both minerals are universal in geographical distribu-tion and their presence implies not only the presenceof copper but of an oxidizing environment.

The original name for the blue basic carbonate ofcopper was azurite, given to it by Beudant in 1824from the ancient Persian word Lajward, meaning bluecolour. Unfortunately, it was changed by Brooke andMiller in 1852 to chessylite, after the French locality.The change was widely adopted but not generally so.In 1980, the confusion it had raised was cleared bythe International Mineralogical Association Commis-sion for Mineralogical Nomenclature, and chessylitewas discredited in favour of azurite.

There are many synonyms which appear in oldliterature but which should be abandoned. They

R. J. King

FOSSILS

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include arménite (of Delamétherie), lasurite (ofHaidinger) and lazurite (of von Kobel). There are oth-ers which are equally confusing, such as azurite (ofJameson), a synonym of lazulite, and azurite (ofWebster) a synonym of smithsonite.

Although the name malachite has long been ac-cepted to describe the green basic carbonate of cop-per, it took several centuries before it was accepted inthat form. Theophrastus, writing in 315 BC (‘onstones’), referred to ‘false emerald’ in copper mines.To Pliny we are indebted in 77 AD for the originalname molochitis, which is taken from the Greek formallow in allusion to the similarity of the colour ofmalachite to the green of the mallow plant. Pliny alsoreferred to ‘smaragdus’ to mean either turquoise or apoor-quality malachite which was much improved by‘washing in oil’ (ancient faking).

In 1546, Agricola, in his Aerugo nativa, referred tomolochit. In Lovell’s History of Minerals, 1661, wesee, for the first time, that the ‘o’s in molochitis havebeen changed to ‘a’s. This change was augmented byWallerius, writing in 1747 on malachit. The suffix itewas added by Dana in 1892. A possible point of con-fusion concerns the use of the name molochite todescribe an artificially modified clay given to it in1986 by Barstow. Molochit has also been used todescribe a type of agate.

There are other synonyms which have little valueor are confusing. They include malachite kiesel,which is chrysocolla; malachite de plomb, which is amixture of malachite and cerussite; and malachitemica, which equals torbernite. Atlaserz (of Breit-haupt) is an old name for fibrous malachite or a mix-ture. A term which should be abandoned forthwithby any self-respecting mineralogist is the lapidaryterm ¢black malachite’, which is chalcedony enclos-ing dendrites of psilomelane.

The environment of azurite and malachiteBoth azurite and malachite are the product of super-gene activity – i.e. the result of surface waters perco-lating through an outcrop of a sulphide body to pro-duce ion-rich waters which promote chemicalactivity lower down a profile. If sufficient carbonate isavailable, azurite and malachite are likely to be pre-cipitated in what is known as a zone of oxidation justabove the water table. The compositions of thegroundwater and the host rocks are genetically criti-cal in determining what secondary minerals form insuch an oxidizing environment.

Whether azurite or malachite is produced undersuch circumstances depends on the available concen-trations of O

2, CO

2 and H

2O. The transition between

the two is a sensitive one. Both are precipitated byneutralization under oxidizing conditions with a pHranging from 6 to 8. Most react more sensitively tochanges of pH than Eh, and the latter is not consid-ered here.

While azurite has a broader range of stability thandoes malachite, it prefers relatively more acidic condi-tions with pH values no more than 6–7. When anincrease of pH occurs – e.g. when mineralizing solu-tions encounter carbonates such as limestone ordolostone – the stability of malachite is more likely toeffect. This explains why malachite is more abundantthan azurite and frequently replaces it as a pseudo-morph. Azurite is produced under a comparativelyrare set of circumstances, essentially by loss of CO

2

and gain of H2O.

The chemistry and structure of azurite and malachiteThe formula of azurite is Cu2+

3(CO

3)

2OH

2, with CuO

69.2%, CO2 25.6% and H

2O 5.2%, Cu = 55.3%. The

structure of azurite contains Cu2+ ions in approxi-mately square co-planar groups with two O2– and two

Fig. 1. A typical crystal ofazurite from the Tsumebmine, in Namibia. Note thebeginnings ofpseudomorphism bymalachite. The length ofthe crystal is 175 mm.(Photo: Lee Boltin.)

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2(OH)1– groups. These square groups are linked intochains parallel to the b axis. Each (OH)1– group isshared by three Cu2+ and each oxygen of the triangu-lar (CO

3)2– is bonded to one copper.

The symmetry of azurite produces fine and some-times large crystals (Fig. 1). Crystals are often com-plex, frequently tabular or short prismatic. Azuritemay be stalactitic, the latter sometimes spiral. It maybe nodular, as sand crystals or hollow nodules linedby small brilliant crystals. It may be massive, encrust-ing or earthy. It is often associated with malachite,the latter replacing it to varying degrees.

The formula of malachite is Cu2+2(CO

3)(OH)

2 with

CuO 71.9%, CO2 19.9%, H

2O 8.2%, Cu = 57.4%. A

cobaltian brownish green malachite has been re-ported from Shaba in Zaire. There is an Mg analoguein the form of pokrovskite Mg

2(CO

3)(OH)

2.0.5H

2O. In

the structure of malachite, Cu2+ is octahedrally co-ordinated by O2– and (OH)1– in CuO

2(OH)

4 and

CuO4(OH)

2 octahedra. These are linked along the

edges to form chains running parallel to the c axis,and these are bonded by triangular (CO

3)2– groups.

The symmetry of malachite is also monoclinic; butunlike azurite, distinct crystals are rare and then onlyform acicular crystals in parallel groups to formsheets. Single crystals may group to form rosettes. Itis commonly massive or encrusting or as mammillaryor botryoidal surfaces (Fig. 2). It may form tuberosemasses with divergent or fibrous crystals. It can formthick deposits with distinct and shaded banding.

Other physical featuresAzurite has two cleavages, one perfect on {011} andanother only fair on {100}. Twinning in azuritetends to be random interpenetration. The colour of

azurite crystals is an intense blackish blue, but fadesto a paler blue in encrusting and earthy habits. Thestreak is usually a lighter blue than the crystals. Thelustre is vitreous in crystals but dull in earthy varie-ties. The density is 3.77 ´ 103 kg m–3 and the hard-ness 3.5–4.

Malachite has one perfect cleavage on {201}, par-allel to the planes of the CO

3 groups, but owing to the

dominant fibrous habit is difficult to see. Malachite istwinned on (100), represented again by the fibroushabit. The colour of malachite is shades of brightgreen, with light and dark shade boundaries inbanded material. Crystallized material is always adarker green than encrusting or earthy habits. Thestreak is always green, but a lighter shade. The lustreis silky in fibrous masses and dull in encrusting orearthy forms. The density of malachite is (3.9–4.03) ´ 103 kg m–3 and the hardness is 3.5–4.

Distinguishing features of azurite and malachiteWhile it is easy to differentiate between azurite andmalachite, even though they often occur intimatelyassociated, there are other species which occur in thesame habitat and are equally associated.

With azurite, the mineral linarite (PbCu(SO4)

(OH)2) is perhaps the most likely to cause confusion.

Its crystals are also monoclinic, but it does not effer-vesce in acids as does azurite. The colour of linarite isusually less intense. There are genetic clues forlinarite. It is more likely to be associated with a sul-phate régime than a carbonate one.

With malachite, the species most likely to causeconfusion is pseudomalachite (Cu

5(PO

4)

2(OH)

4. Like

malachite, it occurs most commonly as reniform orbotyroidal masses with a radial fibrous internal struc-

Fig. 2. A reniform mass ofmalachite from the BurraBurra mine, SouthAustralia. The specimen is65 mm in width. NationalMuseum of Wales, KingCollection 83.41G.M3857.

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ture and concentric colour banding of dark emeraldgreen. While soluble in acids, it does not effervesce inthem. While sometimes associated with malachite, itstands out as a darker shade of green. The symmetryof pseudomalachite is also monoclinic, but crystalsare rare. There are many other species which resem-ble malachite but experience is necessary to differen-tiate between them.

The alteration of azurite and malachiteWhile both minerals are stable in an alien environ-ment such as a mineral collection, continued in-situoxidation subjects them to possible modification, es-pecially in the case of azurite. The latter is then fre-quently modified by malachite to varying degrees,sometimes to crystallographic completion as seen atBroken Hill, New South Wales, and Tsumeb in Na-mibia. The change commences at a centre andspreads across azurite crystals as radiating bandedsilky-lustred patterns (Fig. 1). The reverse changefrom azurite to malachite is rare. Many other miner-als have been reported as pseudomorphs after azurite,including aurichalcite, bayldonite, brochantite,chrysocolla, enargite, plancheite, tennantite and na-tive copper. Fine pseudomorphs of malachite aftercuprite are relatively common, especially from theformer Chessy mine, near Lyon in France.

Some classic localitiesBoth azurite and malachite are geographically wide-spread, howbeit many localities are of locality interestonly and do not obtain classic status. There are somethat do. Unfortunately, most of them are now nolonger productive and one has to rely on museumsand private collections to enjoy the classic materialstored there.

Perhaps the finest azurite crystals ever minedwere from the Tsumeb mines in Namibia, from theupper oxidation zone, in the 1920s and 1930s. Su-perb dark-blue crystals up to 250 mm in length werecollected at that time. Equally famous were thepseudomorphs of malachite after azurite, whichlacked the usual corrosion clues of a pseudomorphbut retained the sharp definition of azurite. Malachitein sharp crystals up to 13 mm, found in cavities inmasses of chalcocite and as spherical aggregates withvelvet-like sheen, were also found at Tsumeb.

While now exhausted, the legacy left by artisansworking with malachite from the several mines of theUral Mountains of Russia proves the enormous valueof the deposits there. Such mines at Gumeshevsk pro-vided masses up to 60 tonnes and at Karpinsk andNizhniy Tagilsk yielded masses of malachite as muchas 14.8 m2 across the upper surface. Inlay work usingmalachite is legendary in the Russian Imperial Pal-aces and in some of the stately houses in Britain,

including Chatsworth in Derbyshire and Waddesdonin Buckinghamshire.

Another famous locality where azurite and mala-chite reached high levels of excellence was the minesof Broken Hill, New South Wales. Perhaps the moststriking material came from the Proprietary andBlock 14 mines, with masses of dark-green velvetymalachite associated with contrasting crystals ofcream-coloured cerussite, and superb short tabularprisms and equidimensional plates of azurite. The lat-ter were considered to be so perfect that they wereused in crystallographic work.

Equally famous was the enormously rich coppermine at Burra Burra in South Australia. Most of theclassical material mined there was pre-1877, butsome was produced in a recent re-opening in 1969.The primary, disseminated sulphide ore body wasoxidized to produce radially and concentricallybanded masses of malachite. The filling of cavities inthe ore body by malachite produced botryoidal andmammillary linings characteristic of the locality(Fig. 2). The South Australian Museum in Adelaidehouses fine material from this locality.

Equally famous, if only for the unfortunate use ofthe name chessylite, is the French locality in theBeaujolais district near Lyon, Rhône, known as theChessy Mines. This is an ancient mining area whichwas probably worked in the Bronze age, but withrecords dating back to 1440. It was in 1811 that amuch richer strata-bound ore body was found andvigorously exploited until 1845. It was during thisperiod that the classic material was produced. Themines were finally abandoned in 1875 and only opti-mistic collectors visit the site now. More rewarding isto pay a visit to the Musée Guimet d’HistoireNaturelle, Lyon. While superb crystallizations of az-urite were produced, the bulk of the material con-sisted of sand crystals cemented by azurite, and some-times by malachite, or as stalactites and nodules withcrystallized interiors. Pseudomorphs of malachite af-ter cuprite were equally famous at Chessy.

Some years ago a large cavity lined with superbazurite crystals was found in Morocco at the Touissitmines near Oujda. Some of the crystals attained alength of 120 mm. Sardinian localities have beennoted for crystallized azurite. Fine material has beenproduced for many years from American mines suchas the Copper Queen Mine, at Bisbee, Cochise County,Arizona, where large ball-like masses of azurite withintergrown malachite occur. There are several impor-tant localities in Africa, such as Katanga in Zaïre,where masses of malachite resembling old Russianmaterial have been mined and the Mashamba WestMine also in Shaba, Zaïre, from where much naturalmalachite now comes for lapidary purposes.

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While fine crystallized azurite and malachite havebeen found in British mines, the oxidized zones havelong been worked out, with little hope that othersmight be found. There are exceptions, such asTynagh in County Galway in Ireland, from wheremuch excellent azurite and malachite has come. Theenormous amount of British mineralogical materialsent abroad for gain during the heyday of mining isbeginning to find its way back home, largely as aresult of the buying attendance of British dealersthrough trade fairs.

While occurrences of both azurite and malachiteare widedspread in Britain, none now attains interna-tional status. An examination of any oxidized envi-ronment, be it an arenaceous one such as aPermo-Triassic horizon or Lower Palaeozoic or Pre-cambrian metasediments, will, if copper is present,yield both species in varying amounts, especially in acalcic environment.

The uses of azurite and malachiteThe principal use of both azurite and malachite is asa rich ore of copper, and thousands of tonnes of po-tential cabinet material has been crushed and fed intosmelters. Fortunately, representative material hasbeen saved to grace mineral collections worldwide.Apart from the aesthetic appeal, both species, mala-chite in particular, have long been used in medicalalchemy and as a gem-quality lapidary medium.Medically green ‘stones’, including malachite, havebeen reserved for eye disorders or as a local anaes-thetic.

Both azurite and malachite when finely groundand mixed with oils have been used extensively as asource of blue and green pigments, especially in an-cient wall paintings up to the 17th century. At thispoint it should be pointed out that confusion mightoccur with regard to the use of the modern termmalachite-green, which is an artificially manufac-tured dyestuff of the rosaniline group.

Both azurite and malachite have been used exten-sively through time for ornamental purposes. Owingto their intense blue colour, crystals, if transparent,have been attractive to the gem cutter but only toproduce specimen facets. Malachite has been usedvigorously for ornamental work, inlay work and per-sonal jewellery where advantage is taken of its in-tense green colour and its intricate internal structure,providing colour variation and shape. It is said thatdarker colours take a better polish. There are prob-lems in such wear. Malachite tends to be brittle andcare should be taken with ornaments and pendants.Malachite jewellery blackens in time if worn againstthe skin. A little vinegar added to a polishing mediumis usually effective in removing the discoloration. Al-though a matter of taste, the so-called azurmalachitehas proved to be a popular medium.

Most classic localities referred to above are nowexhausted and the bulk of natural lapidary malachitenow comes from such places as Zaïre, Eilat in Israel (are-discovery of the ancient source used by Greek andRoman artists) and the Elacite mine in Bulgaria.There is sporadic production from some Americanmines such as Globe at Bisbee in Arizona and fromthe Rosita mine in Nicaragua, Central America.

The faking of azurite and malachiteWhile it is unusual for azurite to be falsified, that isnot the case with malachite. There are three synthe-sized textural variants which are almost impossible todifferentiate from natural malachite. They are syn-thesized in Russia by crystallization from aqueoussolutions on a highly profitable basis. Such syntheticmaterial is readily available by the kilogram fromlapidary material dealers.

Only the use of thermograms appears to be ofvalue in distinguishing between natural and syn-thetic. The process of synthesis is well established andthe only way one can be sure that an ornament is innatural malachite is if it is declared to be an antique.

The curation of azurite and malachiteLittle need be said about the care of both minerals;they should be perfectly stable in normal situations.The greatest enemy of both is dust. If cleaning shouldbe necessary, malachite will benefit from cleaning indistilled water to which is added a little low-strengthammonia, followed by rinsing in clean water. Theprocedure should not be employed on the lapidarist’sazurmalachite, when clean water only should beused.

Suggestions for further readingde Fourestier, J. 1999. Glossary of Mineral Synonyms.

Canadian Mineralogist Special Publication 2.435 pp.

12th Mineralogical Symposium. 1991. Azurite andother copper carbonates, Mineralogical Record,v.22, pp.65–69.

Palache, C., Berman, H. & Frondell, C. 1951. Dana’sSystem of Mineralogy, 7th edition.

Vink, B.W. 1986. Stability relations of malachite andazurite, Mineralogical Magazine, v.50, pp.41–47.

Wilson, W.E. (ed.) 1977. Tsumeb, the World’s GreatestMineral Locality. Mineralogical Record. 129 pp.

Hard science: ‘You’re sitting there watching [on an OpenUniversity programme] soothing pictures of lava floes [sic] onSkye … But then the presenter chips in with a confusing graphicand something like the following: “At shallower crustal levelsthese parental basaltic magmas experienced fractionalcrystallisation to yield a silica under-saturated, netherenenormative basalt bemanite association and a silica saturatedbasalt trachite association.” Already with the parental basalticmagmas! Just not so loud, all right?’ – Stuart Jefferies, TheGuardian, 15 February 1997.

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Azurite and Malachite

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