This specimen is from a find that produced khomyakovite, manganokhomyakovite and ferrokentbrooksite (all verified via WDS). However, most crystals were found to be zoned, with ferrokentbrooksite cores and khomyakovite or manganokhomyakovite shells – or just plain ferrokentbrooksite alone. It is impossible to distinguish the various possibilities visually.
A qualitative EDS scan for this sample shows the presence of W. (See the “Analysis” tab.) The W peak may not look very impressive, but, according to the analyst, the high energy peak of W is relatively hard to detect with his equipment , so it is actually “significant”. (The low energy W peak is “buried” under the Si peak.) If the W is in the proper structural site and there is enough of it, this could be khomyakovite. If not, it is probably ferrokentbrooksite. EDS is not sufficient to decide. WDS – very expensive – would be needed. Khomyakovite is extremely rare. Ferrokentbrooksite – not so much.
Of the half dozen or so specimens from this find which I was fortunate enough to have properly analyzed, about half had khomyakovite or manganokhomyakovite, the rest only ferrokentbrooksite. If you think of this as a lottery ticket, that’s pretty good odds. But it isn’t a guarantee.
The specimen features several small, but well formed crystals to about 1.5 mm. You will need 15-20X to view them clearly.
The first photo (FOV 4.0 x 4.5 mm) shows a group of crystals, the largest 1.5 mm long, spanning a bit < 2 mm altogether.
These same crystals are shown in the next pair of photos (FOV 4.9 x 4.5 mm). The black needle is an amphibole (probably actinolite-tremolite series.) The tiny white crystals are natrolite. The black stuff is molybdenite seen nearly edge on. The matrix is feldspar – probably albite.
As shown in the fourth photo (FOV 4.3 x 6.0 mm), there are also numerous small, but attractive, titanite crystals and small, but very sharply formed, amphibole crystals (likely actinolite-tremolite). The EGM crystal in this photo is about 1.3 mm in diameter.
The fifth photo shows a pair of crystals 1.4 mm in diameter. One or both appear to be irregular or dinged.
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