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Please help! Shiny dark green crystals
  
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DanielJP




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PostPosted: Sep 25, 2020 08:38    Post subject: Please help! Shiny dark green crystals  

I found this specimen and a lot of others nearby on a ridge in the San Bernardino mountains. Most of the surrounding rock seemed to be gneiss. This was in the San Gorgonio Wilderness if that helps, around the NW part of it. What is it??? Looks like it’s in feldspar.
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DanielJP




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PostPosted: Sep 25, 2020 08:58    Post subject: Re: Please help! Shiny dark green crystals  

I apologize, getting used to this website. Trying to reply with a photo,!


6608CD07-68AF-48D0-AF78-9CCCC22D32AE.jpeg
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DanielJP




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PostPosted: Sep 25, 2020 09:05    Post subject: Re: Please help! Shiny dark green crystals  

Little closer


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Bob Carnein




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PostPosted: Sep 25, 2020 09:14    Post subject: Re: Please help! Shiny dark green crystals  

The somewhat diamond shaped cross sections on some of the crystals, combined with apparent cleavage, suggest an amphibole. The amphiboles and pyroxenes are among the most difficult minerals to ID and classify; unfortunately, a picture doesn't provide enough information for a positive ID.
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alfredo
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PostPosted: Sep 25, 2020 09:18    Post subject: Re: Please help! Shiny dark green crystals  

Perhaps an Amphibole? You'd need to check the cleavage angles to be sure.
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DanielJP




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PostPosted: Sep 25, 2020 09:27    Post subject: Re: Please help! Shiny dark green crystals  

Oh boy... bit off more than I could chew
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alfredo
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PostPosted: Sep 25, 2020 11:42    Post subject: Re: Please help! Shiny dark green crystals  

No worries, Daniel. We all started out like that!

Some minerals tend to break along certain flat parallel planes, rather than just random fractures in any direction. We call these parallel planes of breakage "cleavages". When you slowly tilt your piece outdoors in the sun, while concentrating on a single one of those dark green crystals, there will come a point in which you'll be holding it at just the right angle for all those parallel cleavages to reflect the sun at you at the same time, a flash reflection. Then you'll know you found the cleavage. (Minerals that don't have any obvious cleavage planes, like quartz, won't show this effect.)

Amphiboles have 2 such cleavage planes, separated by 120 degrees, so if you keep on rotating your specimen in the sun, you should see a second flash.
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Riccardo Modanesi




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PostPosted: Sep 25, 2020 14:56    Post subject: Re: Please help! Shiny dark green crystals  

Hi to everybody! If amphibole: hornblende; if pyroxene; diopside. My opinion: diopside.
Greetings from Italy by Riccardo.

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Hi! I'm a collector of minerals since 1973 and a gemmologist. On Summer I always visit mines and quarries all over Europe looking for minerals! Ok, there is time to tell you much much more! Greetings from Italy by Riccardo.
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DanielJP




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PostPosted: Sep 25, 2020 15:21    Post subject: Re: Please help! Shiny dark green crystals  

Ah I see!! Thanks for that bit of information! I tried posting a gif of me tilting it, but it definitely shows these cleavage flashes! Is there a way to measure those angles as well as tell tale angles that could identify the mineral??
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DanielJP




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PostPosted: Sep 25, 2020 15:23    Post subject: Re: Please help! Shiny dark green crystals  

Bahhh!! Sorry I am just not processing that information fully yet! I get it. So how can I measure the angle? Or is it just by guesstimating the angle? I did well in trigonometry!! XD
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Kevin Schofield




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PostPosted: Sep 25, 2020 15:47    Post subject: Re: Please help! Shiny dark green crystals  

DanielJP wrote:
Bahhh!! Sorry I am just not processing that information fully yet! I get it. So how can I measure the angle? Or is it just by guesstimating the angle? I did well in trigonometry!! XD


Pyroxenes (in this case as has been suggested likely Diopside) have two cleavages at right angles. The Amphiboles (as Riccardo suggests probably hornblende) are at 120 degrees. Even without a protractor, that's easy to spot.

I believe that in your first picture the crystal that appears darker than the rest around 3/4 way down in the middle (just above the shadow) clearly shows two lineations that are probably cleavage that are at 60/120 degrees, so I think you have a hornblende-bearing rock.

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alfredo
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PostPosted: Sep 25, 2020 16:25    Post subject: Re: Please help! Shiny dark green crystals  

I agree with Kevin that these are probably amphiboles, but obnoxiously pedantic curmudgeon that I am, I'd like to introduce a warning about using the name "hornblende":
The amphiboles (or rather our knowledge about them) have evolved into an extremely complex group of closely related minerals, over 200 species currently and growing every year, and often quite difficult to distinguish even when holding an analysis in one's hand! Many of the things we used to call "hornblende" in college decades ago are now reclassified under other names. So I'd be very careful about writing Hornblende on a label; just Amphibole would be safer. For more information, go to the Mindat page and scroll down to the species list:
https://www.mindat.org/min-207.html

They say scientists, collectors and curators are either lumpers or splitters. I tend to be a lumper myself, so I use the broad name Amphibole. The splitters will have to find a professional mineralogist with abundant free time on their hands (ha ha ha!) to do the necessary analyses on their quarter-million-dollar machines to tell you exactly which of those 200 species you have.

Kevin, you're very lucky you have amphibole expert Dr Marian Lupulescu not too far away in Albany. He has done a tremendous job systematically analyzing the amphiboles in the Hudson Highlands. You have surprisingly lots of different amphibole species in your region, although they don't look that much different from each other visually.
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Steve Maslansky




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PostPosted: Sep 25, 2020 18:40    Post subject: Re: Please help! Shiny dark green crystals  

Thus might help. Geology of the San Bernardino National Forest,
https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5207093.pdf
(link normalized by FMF)
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