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23 Jul-02:15:45 Re: black, metallic, yellow oxide? (Tobi)
23 Jul-02:03:58 Re: help identify this rock. Sapphire?? (Tobi)
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Black, metallic, yellow oxide?
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Linus




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PostPosted: Jul 21, 2021 14:51    Post subject: Black, metallic, yellow oxide?  

Hi All! This is one I probably should know, but its not registering.
pyramidal, Black, sparkly metallic on broken surfaces, strong cleavage, non-magnetic, larger broken surfaces that cut across the crystal seem to be oxidizing to yellow crusts... not sure if it is radioactive or not, location unknown. Ive seen a couple of these that were 5 - 8cm tall. Any thoughts?



20210721_123737[1].jpg
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20210721_123737[1].jpg



20210721_123709[1].jpg
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20210721_123709[1].jpg


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Bob Morgan




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PostPosted: Jul 21, 2021 15:06    Post subject: Re: black, metallic, yellow oxide?  

Could it be sulphur in a limonite pseudomorph of pyrite?
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SteveB




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PostPosted: Jul 21, 2021 15:35    Post subject: Re: black, metallic, yellow oxide?  

Magnetite? Yellow oxide it often zinc related and here it may have nothing to do with the crystal itself but from the host matrix. Could be residue from “YellowTak” similar to “BluTak” that rubbery gum stuff you use to stick posters to your wall. Its commonly used to “stick down” mineral samples into small cases. If it is it could be crumbly or maybe still sticky depending on how old it is.

Did you yourself collect this in the field? Where exactly? Or was it given to you or did you buy it? The yellow I’m certain is related to previous adhesive material and nothing to do with mineral. More testing needed like mentioned in the sticky forum thread on what to do before posting a photo and asking what is this. It wastes everyones time and discourages relevant answers. So read that thread and host back with more data.

My guess for now is magnetite. Just a guess.
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Matt_Zukowski
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PostPosted: Jul 21, 2021 15:50    Post subject: Re: Black, metallic, yellow oxide?  

Another wild guess - could it be franklinite? Strong cleavage argues against franklinite. What is the hardness, streak, and SG?
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Linus




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PostPosted: Jul 21, 2021 16:01    Post subject: Re: Black, metallic, yellow oxide?  

I stated it was non magnetic, very strong cleavage too, as shown, almost looks like carbonate type cleavage...
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Linus




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PostPosted: Jul 21, 2021 16:12    Post subject: Re: Black, metallic, yellow oxide?  

Matt, I think Franklinite is an excellent guess... I'll play with a bit more.
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Linus




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PostPosted: Jul 21, 2021 17:31    Post subject: Re: Black, metallic, yellow oxide?  

Hardness is between 4 and 5 (done with hardness points) and it seems to have at least three pronounced cleavage planes... so probably not franklinite. It is not fluorescent.
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Matt_Zukowski
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PostPosted: Jul 21, 2021 18:48    Post subject: Re: Black, metallic, yellow oxide?  

It would be really good to get a streak and a SG. Are you able to do these things? If you don't have a balance beam setup to do SGs, i can tell you a way to do it with just a cheap jeweler's scale and a measuring cup if you want.

Also, is it cubic, tetragonal, or orthorhombic? I thought it was cubic but pictures can deceive.

Another wild ass guess - cuprite like maybe from Rubtsovsk. Perfect cleavage again argues against this guess but at least curpite has some cleavage.
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Linus




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PostPosted: Jul 21, 2021 19:21    Post subject: Re: Black, metallic, yellow oxide?  

Sort of cubic, but there is a flattening at the pyramid base that is offset versus the opposite side, so maybe not cubic? (I haven't had mineralogy in about 40 yrs). It is noticeably heavy. I may be able to do a spg in the next day or so. Streak is a sub-metallic red brown. This piece, along with several similar others came to me from an estate - we have absolutely no location info available. thank you very much for the ongoing feedback.
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Linus




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PostPosted: Jul 21, 2021 19:24    Post subject: Re: Black, metallic, yellow oxide?  

oh, and the whitish spots in the picture look to me slightly aplitic, they fluoresce a weak tan-yellow.
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Bob Carnein




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PostPosted: Jul 21, 2021 19:55    Post subject: Re: Black, metallic, yellow oxide?  

How about sphalerite? It should have a pale tan to brown streak and 6 directions of cleavage (seldom easily counted). The "other" mineral could be a break-down/alteration product of sphalerite (maybe smithsonite or hemimorphite). A streak would definitely help--try it on the bottom ridge of one of your wife's teacups (but don't tell her I said to do that!?)/
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Pete Richards
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PostPosted: Jul 21, 2021 20:28    Post subject: Re: Black, metallic, yellow oxide?  

the first one suggests brookite (orthorhombic) altering to earthy anatase. The second one does not....

I don't know how this fits with the apparent cleavages.

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Linus




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PostPosted: Jul 21, 2021 20:37    Post subject: Re: Black, metallic, yellow oxide?  

Hi Bob, I think youre right about the orthorhombic, but the streak and pronounced cleavages suggest other than brookite... I think we're closing in on it!
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Tobi




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PostPosted: Jul 22, 2021 03:47    Post subject: Re: Black, metallic, yellow oxide?  

The second photo made me think of scheelite, the shape would fit, also the hardness between 4 and 5 and the fact that is is "noticeably heavy". But the streak and the fact that it is not fluorescent would not fit ... :-/

I hope someone can solve that riddle!

Regards
Tobi
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Linus




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PostPosted: Jul 22, 2021 15:20    Post subject: Re: Black, metallic, yellow oxide?  

well, we are closing in on it. XRF (Niton XL5) shows strong tungsten and iron... see the pic.


pyramidal.jpg
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Linus




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PostPosted: Jul 22, 2021 15:30    Post subject: Re: Black, metallic, yellow oxide?  

ferberrite ps scheelite???
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Linus




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PostPosted: Jul 22, 2021 16:58    Post subject: Re: Black, metallic, yellow oxide?  

... one of Rob's pieces... (oh and the yellow may be tungstite or similar...

"Ferberite Pseudomorph after Scheelite
Ferberite Pseudomorph after Scheelite from Trumbull, Fairfield Co., Connecticut

Collection
Robert Lavinsky

Description
An excellent Ferberite crystal over Scheelite, where the crystal replaced the original mineral. This material came out over 100 years ago, and is considered one of the most classic of East Coast "black uglies," and quite hard to obtain today. This is one of the largest examples, and certainly the best and largest single crystal that I have seen for sale myself by a long run. It is remarkably complete, if a bit crude on some faces, all around.

Locality
Trumbull, Fairfield Co., Connecticut

Dimensions
4.6 x 3.9 x 3.7 cm."
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Tobi




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PostPosted: Jul 23, 2021 02:15    Post subject: Re: Black, metallic, yellow oxide?  

I'm glad that I maybe wasn't that wrong with my scheelite guess ;-)
Linus wrote:
ferberite ps scheelite???
I think we're on a good way. The ferberite ps. after scheelite - the so-called "reinite" - could really fit: Hardness between 4 and 5, very heavy, non-fluorescent, brownish streak, good cleavage, contains tungsten and iron ... and the crystal form would also match ...
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Susan Robinson




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PostPosted: Jul 23, 2021 07:27    Post subject: Re: Black, metallic, yellow oxide?  

My first guess was a pseudomorph of ferberite or hubnerite after scheelite from Trumbull, CT. Ron Januzzi had a big collection of these at his old rock shop near Brewster, NY, back in the 1980s.

Susan Robinson

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Linus




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PostPosted: Jul 23, 2021 17:34    Post subject: Re: Black, metallic, yellow oxide?  

with precious little info, I think you did great, than you!
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