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Tunellite

Posted by Rock Currier  
avatar Tunellite
June 29, 2009 07:34AM
Click here to view Best Minerals T and here for Best Minerals A to Z and here for Fast Navigation of completed Best Minerals articles.


Can you help make this a better article? What good localities have we missed? Can you supply pictures of better specimens than those we show here? Can you give us more and better information about the specimens from these localities? Can you supply better geological or historical information on these localities?



Tunellite
SrB6O9(OH)2ยท3H2O monoclinic

1.Tunellite crystal ~8cm wide©


By far the finest crystals of Tunellite yet found are from Boron, California. One of the best and largest know in pictured above. Larger crystals have been found, but they tend to be rather complex and do not have good crystal shapes like the one pictured above. Some of these complex crystals are up to about 15 cm in diameter but do their complex nature it is difficult to say if they are all part of the same crystal. Typically these complex Tunellite crystals are associated with Ulexite. Tunellite is one of the more stable borates, and unlike Colemanite and Ulexite crystals of Tunellite seem to retain their luster over long periods of time. Tunellite has been found at a number of other localities including localities in 'Turkey and Argentina and has been sparingly found in the Corkscrew mine in Death Valley, but the specimens are rather nondescript. We do not have any information about the Tunellite specimens that have been found in Turkey.
[Rock Currier 2009]

Tunellite
USA
California, Inyo Co., Boraxo Mine (Kern Borate; Boraxo Deposit; Boraxo No. 1 and No. 2; Clara Claim; Thompson Mine; Tenneco Mine)

2.Tunellite ~8cm wide©


Very little Tunellite was found at this locality. Probably fewer than a flat full of specimens and this may be the best one. The mine is much better know for its wonderful big white shiny blocky Colemanite crystals and its fine specimens of Hydroboracite. Notice the color of the "mud/dirt/matrix in this Tunellite specimen and compare it to the color of the mud/dirt/matrix from the specimens from Boron below. You can usually identify the specimens from Boron by the distinctive color of the "mud" on its specimens.


Tunellite
USA
California, Kern Co., Kramer District, Boron, U.S. Borax Open Pit Mine

3.Tunellite crystals in mud, ~15cm wide©



4.Tunellite & Ulexite ~11cm wide©
5.Tunellite & minor Ulexite ~10cm wide©


6.Tunellite on Ulexite ~7cm wide©
7.Tunellite in mud ~4cm tall©


8.Tunellite & Ulexite ~5cm across© Peter Kohorst
9.Tunellite in Hydroboracite FOV 1.8cm© Elmar Lackner


The best Tunellite crystals were found in the early days of the open pit mine (late 1950s) when a group of mineral collectors, members of a Los Angeles, California mineral club were collecting on the dump. One of them noticed some attractive well formed shiny white crystals in some of the distinct blue/green/tan mud that had been dumped by one of the big mine haul trucks. Soon they were all collecting specimens as fast as they could find them. Probably two or three hundred well formed crystals were collected. Almost all of them were removed from the mud like matrix. Perhaps the best and perhaps the only surviving specimens with the original distinctive Boron mud matrix is shown in picture#3 above. Over the years other kinds of Tunellite specimens have been found at boron, but they have always been rather rare.

Most of the Tunellite specimens show somewhat complex crystals associated with Ulexite as exampled by pictures 4, 5, & 8 above. Some of the specimens can be as much as a foot across with bulk of the specimen being the typical intergrown fibrous Ulexite almost always somewhat discolored by the mud that is everywhere present in the deposit. It is not really mud till you get it wet, but you get the picture I think. A particularly rare form of Tunellite are the bright shiny crystals that are found on Ulexite. See picture 6 above. More accurately they are found growing in among needles of acicular Ulexite and are exposed by brushing away the needles of Ulexite. Probably fewer than twenty of these specimens exist. Another type of Tunellite specimen was found at Boron during the early days and these were little flat blade like crystals of Tunellite like the ones in picture #9. These were associated with sharp micro needles of Hydroboracite. The crystals never got larger than about 5mm, but some specimens showed nice shiny white crystals of Tunellite and Hydroboracite. The one pictured above looks like it has never had a bath, and the Hydroboracite at the base of the Tunellite crystals is dirty form the ever present Boron "mud". Much finer specimens of this type exist and we will hopefully eventually be able to scare up a good picture of one to include in this article.
[Rock Currier 2009]

Here is a description by the mine geologist Joe Siefke of the last good find of Tunellite specimens at Boron: The last significant Tunellites I'm aware of was a hanging wall occurrence of tunellite. It was a chance find of my own in October, 1998. I was doing map recon near the toe of the massive 1997-98 pit north wall slope failure (35 million tons) when I came upon some vitreous cleavage flakes of tunellite. After that encounter I paid many lunchtime visits to the site (pick, shovel, bars, hammers, boxes, newspapers - you know the drill!). Over a couple of months I accumulated a few hundred specimens of mostly single crystals of roughly spherical shape ranging in size from 1/2 to 4 inches. Some are attached to ulexite; most were floaters in claystone. They appear to have formed in the recesses of the knobby top surface of a thick ulexite bed and arranged along a north-south structure for perhaps 150 feet length by 50 feet width. It was fun while it lasted.



Click here to view Best Minerals T and here for Best Minerals A to Z and here for Fast Navigation of completed Best Minerals articles.

Rock Currier
Crystals not pistols.



Edited 7 time(s). Last edit at 11/18/2010 10:47PM by Rock Currier.
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