Crystal system:            Monoclinic                                Hardness:         3,5 - 4

Density:                        3.83 average                             Cleavage:         perfect

Streak:                         light blue                                   Colour:             blue to very dark blue.

Occurrence:                 A secondary mineral found in the oxidized zones of copper-bearing ore deposits.

Habitat:                        Crystals are usually massive, prismatic, stalactitic, or tabular.  There are over 45 well-known forms and over 100 forms have been described.

Composition:               carbonate                                     Cu₃(CO₃)₂(OH)₂

Amazingly azurite has never been featured as the “Mineral of the Month”.  Of all the minerals this is probably my favourite mineral, so here goes.

The mineral azurite owes its name to its azure-blue colour.  It is also known as Chessylite after the type locality at Chessy-les-Mines near Lyon, France where it was found in 1824.  The oldest reference to this mineral that I could find dates back to 1747.  It was, however, mined since the 12^th century in Saxony, in the silver mines in the area. 

Pseudomorphs of green malachite after azurite are common.  Associated minerals include malachite, calcite, cerussite, quartz and cuprite, to name only a few.  During the Middle Ages azurite was crushed and the powder used as blue pigments in paints by artists, causing peculiar situations where the sky in old paintings, now centuries later, appears green.

World-wide localities include Greece, Germany, England, Australia, Mexico, U.S.A (Bisbee), China, Morocco, Zimbabwe, South Africa and of course the Tsumeb mine in Namibia.

Having to choose a mineral that epitomizes Tsumeb, it would have to be azurite.  These are not my words but those of Georg Gebhard, who needs no introduction.  But as mentioned by Charlie Key in the Tsumeb issue of the Mineralogical Record in 1977, there are no more than about 50 great Tsumeb azurite specimens in all the mineral collections in the world.  The first great find was in 1929, when crystals up to 30 cm were found on the 8^th level.  Another important and rich pocket of azurite was found in the 1980’s.  Although azurites were found during all the periods of mining, they all came from the upper levels, from the first oxidation zone.  All azurite specimens occurred within the zone extending from the surface to a depth of 400 m.  The reason for a nearly continuous supply of azurite over the years is that the deep and upper levels were always mined simultaneously.  The carbonatic ore, present as azurite and malachite from the first oxidation zone was needed as a necessary compound for the smelter to add to the sulphide ore coming from the deeper levels.

The largest azurite crystals recorded from Tsumeb, and also in the world, have reached 50 cm in length, but these crystals were dull.  An exception is the large specimen that was kept at the Newmont Mining Company’s office in New York for many years.  This specimen, with up to 15 cm crystals, shows partial alteration to malachite on most of the big crystals. This famous specimen has a history of its own.  It belonged to a miner who could not pay his beer tab at the famous Eckleben hotel in Tsumeb.  The owner of the hotel took the specimen in lieu of the money, a deal which could hardly be called equivalent as the value of the azurite exceeded the bill a few thousand times. This azurite specimen was later bought back by the miner.

A unique find was made in the eighties when free-standing, needle-like, brilliant blue crystals up to 7 cm were found.  These provided dramatic contrast with the matrix of emerald green arsentsumebite.

Some of the finest azurites known originally belonged to the collections of mine manager, F.W. Kegel and his mine captain, Wilhelm Klein.  These specimens are now in the collections of the Smithsonian and Harvard, respectively.  All these specimens were found on the 8^th level.

During Easter in 1994 the world famous “Easter Pocket“, was discovered on the 8^th level.  This find also has a very interesting story to it, which is unfortunately too long to include in this article.  This pocket was 2 m long and 80 cm wide and was filled with purple-blue azurite crystals, nearly all completely crystallized and forming a blue, three-dimensional network with unique crystal formations different to all the previous finds.  As luck would have it the blast left the contents of the cavity intact, but the detonation opened it up clearly. The finder was able to pick some of the finest crystals ever seen, like apples from a tree.  Statistically this pocket broke all known statistics on distribution of quality.  Normally only 1 to 5 % of a find is exceptional. But in this case a third of the find was of unsurpassed quality.  The quality of the next third was similar to those azurite specimens that are called very good, while the remaining specimens were average, but it was still better than the azurites in most of the rest of the world’s collections.     JDJ

References

Bancroft, Peter, (1973) – The World’s Finest Minerals and Crystals.                                Gebhard, Georg, (1999) – Tsumeb II.

www.webmineral.com                       www.mindat.org                       www.minerals.net                         http://en.wikipedia.org