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The Kestelek borate mine with "Giant Crystal Project" author in foreground

Photo : Giant Crystal Project / S. Yuecekent

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Probertite - Probertit - Probertite - Probertita

Asia : Turkey : Probertite crystals up to 1 m size and large colemanite crystals from the Kestelek mine, Turkey

Coordinates : 39°56'N , 28°33'E : Kestelek Borate Mine, Bandirma Province, Western Anatolia, Turkey

Turkey is a most fascinating country. You find an extremely rich cultural heritage, both ancient and modern, a wealth of natural wonders like the Pammukale sinter terraces and the unique tufa landscape of Cappadocia...and an extremely diversified geology. This country is also well endowed with rich mineral deposits, many of which are still undeveloped. However, the turkish borate mining industry is thrieving since many decades and in fact Turkey hosts about 70 % of the worlds borate reserves.

Borate minerals are a somewhat neglected mineral class under mineral collectors and mineralogists alike. Maybe it is for their rather uniform appearance, displaying mostly colourless to white crystals or nodules, that they got little attention in the past. But their industrial importance is immense and even still growing. Like carbon - and to a lesser extent silicon - boron is able to form complex sheet like or three dimensional molecules. More, it also connects easily to other elements like nitrogen, phosphor and carbon. So you find a vast array of different borates in your daily life such as in washing powder, fibre glass and abrasives. And did you know, that the hardest known substance - even harder than diamond - is boroncarbide ?

Some of the borates form nice crystal specimen, but due to their general scarcity they are not too well known. These crystals may get large. Kernite crystals up to several meter size (see the list for a photo) are known to occur in the Kramer borate deposit in California. In the Kestelek borate deposit large colourless to white colemanite crystals up to 5 cm are abundant and may reach up to 40 cm at times. Back around 1980 another seam of ulexite yielded large probertite crystals up to 1 m length. Though this ulexite seam is now long mined out and gone, the mine officials of that time were wise enough to keep one of the largest probertite crystal group mined as display specimen.

The formation of these enormous borate accumulation is despite intense geological research still not very well understood. The borate seams, which may be several meters wide, are almost always part of a volcanosedimentary sucession. So the borates are most probably of volcanic origin. But where does all the boron come from...? And if they are of volcanic origin, why do we find so little of them on a worldwide scale...?

For another turkish locality with giant epithermal calcite crystals please click here and for an interactive & panoramic voyage to some turkish world heritage sites please click here.


Kestelek Borate mine in a nutshell :


Mineralogy :

Borate deposits with ulexite, probertite, colemanite

Crystal Size :

Probertite sprays of up to 1 m and large colemanite crystals confirmed

Geology & Origin :

Volcanosedimentary sucession with some borate seams.

Status :

The probertite crystal finds are historic and date around 15 to 20 years back, while the borate mine itself is still active.

Remarks :

The mine currently is in danger of abandonment despite quite large reserves.



Other notable probertite occurences :

Note : Probertite is generally a rare borate mineral, which occurs only at a few places worldwide

- Probertite is a common constituent of the Calffornian borate deposits such as Ryan, Inyo County and the Baker mine at Boron, Kern County which is also the type locality

- By far the best crystals - freestanding thick crystals with well determined faces up to 12 cm long - occur at the now defunct Kohnstein quarry near Niedersachwerfen, Thuringia, Germany.

- Other, minor occurences include Cheverie, Nova Scotia and the Tincalayu boron deposit in Argentina


Large 1 m spray of probertite crystals on display in the Kestelek mine office

Photo : Giant Crystal Project


Close-up of the probertite spray shown above

Photo : Giant Crystal Project


0,4 m large colemanite crystal from Kestelek on display at Izmir University

Photo : The Giant Crystal Project



Resources and relevant weblinks :

For more information on the mineral probertite please look at, Webmineral and the german Mineralienatlas.

There is only very little information provided on this locality outside Turkey.




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