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Magnesite - Imitations and Misnomers

Dyed magnesite can easily be confused with genuine Turquoise

© K. Sieber, www.makrogalerie.de

 

The magnesium carbonate magnesite [MgCO3] is a rock forming mineral wich occurs in large masses or in nodular aggregates. The most common color is white or grey, less often beige (trade name: »Ivoryite«). 

 

Magnesit

Fig. 1: green magnesite is often mistakenly sold as »jade«

Photo: K. Sieber, www.makrogalerie.de

A contamination with nickel causes green colors in magnesite. This so-called »nickel magnesite« is sometimes sold under the misleading trade name "Apple Jade". Thus, it joins the long list of fake-jades, in which every green mineral ends up sooner or later.

Solid solution serie

Magnesite is mixable with the calcium carbonate calcite [CaCO3] in any ratio and forms a solid solution serie. Calcium-magnesium carbonates with a mixing ratio of 30 - 70% Mg are called dolomite.

Gray-white magnesite with a coarse-grained growth structure which resembles pine nuts or ice flowers in shape, is known as "pinolite" or "ice flower magnesite".

»Pinolite« (ice flower magnesite)

eisblumen magnesit

Fig. 3: »Pinolite« - The resemblance to pine nuts gave this magnesite rock its name.

Photo: K. Sieber, www.makrogalerie.de

The Sunk/Hohentauern deposit in Styria (Austria) is known worldwide for a rock forming magnesite with a typical coarsely crystalline growth structure which resemble pine nuts or ice flowers in shape. Because of this special texture the rock was named »Pinolite« (pignolia = pine nut) or "ice flower magnesite". Large, bright magnesite crystals are embedded in a gray, fine-grained matrix rich in inorganic pigment.

Until 1963 the rock was mined as decorative rock and marketed under the name "Sunk" (the name of the finding place). Today it is found almost exclusively in arts and crafts objects or as tumbled stones.

 

»Lemon Magnesite« (nickel magnesite)

zitronenmagnesit

Fig. 4: partially silicified magnesite

Photo: K. Sieber, www.makrogalerie.de

When larger quantities of this green rock appeared on mineral fairs in the USA for the first time in 1996, it was called "Lemon crysoprase". The eastern goldfields of the Central Division Mine in Western Australia was given as the deposit location.

Chemical and mineralogical analyses have shown that it is a light green, partially silicified magnesite, with colorless quartz in its cracks.

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Possibilities for confusion with other gemstones

There is a high risk to confuse the calcium carbonate magnesite with the calcium silicate howlite. Both occur as a compact, white to beige aggregate or as porous, chalk-like rock. Nowadays yy far the largest part of the tumbled stones and jewelry stones offered as howlite, consists of magnesite. Howlite and magnesite can be distinguished by means of the carbonate test. A small sample of pulverized magnesite, which is best produced by scratching with a hard object over the surface, reacts with 10% hydrochloric acid by forming gas bubbles. Howlite on the other hand does not react.

 

Fig. 5: Lookalikes: howlite [left] and magnesite [right]

Foto: K. Sieber, www.makrogalerie.de

 

Imitations

There are currently no imitations for magnesite. However, the mineral itself serves as an imitation for opaque gemstones like howlite or (dyed blue) Turquoise.

Fig. 6: Magnesite dyed blue is a very widespread Turquoise imitation.

Foto: K. Sieber, www.makrogalerie.de

 

 


Author: Dipl.-Min. B. Bruder

© INSTITUT FÜR EDELSTEIN PRÜFUNG (EPI)