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Post by genchaos on May 9, 2007 11:53:25 GMT -5
This was found in a highly mineralized dike in Arizona. Surrounding matrix is quartz and andradite garnet with what I think are hematite blossoms (but also look like ilmenite). This is supposed to be in an iron/titanium deposit but surrounding mines have nearly every metal imaginable--primarily copper and lead. It might be a morph but the beveled edges are still throwing me off.  |
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Post by geodepat on May 9, 2007 19:07:16 GMT -5
The lines on the top of the crystal remind me of toumaline, but the color looks like garnet or if it was a shinier face I would think rutile. Pat
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Post by Jbeckert on May 10, 2007 15:07:28 GMT -5
Looks to me like a limonite pseudomorph, lots of them up here in PA after pyrite. Some locations even have those beveled edges I think its called Pyritohedral limontie pseudomorph after pyrite. Check the page on mindat for Fruitville Pike, Lancaster county, PA. This would make sense coiming from an iron ore mine area. Good luck!
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Post by Jbeckert on May 10, 2007 15:14:56 GMT -5
Here I found this:
"While "limonite" is amorphous, a number of minerals are noted for decomposing to it without losing their crystal shape - particularly pyrite crystals. Any "crystals" of "limonite" are actually pseudomorphs of other minerals which have decomposed in this fashion"-mindat.org
I just did a quick streak test for the limonites I was speaking of, they seem soft, and streak a dark brown. I didnt go into a hardness test, I had a penny so I guess its higher than 3. Maybe this will help you check it if you have extra material. Oh and I'd agree with Pat being that there is a chance of rutile...
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Post by genchaos on May 10, 2007 15:41:54 GMT -5
I think you nailed it, jbeckert. I looked it up on mindat and it fits perfectly. The pictures and description also matched many of the other specimens I have. I was fixated on titanium because of another opinion I got locally. I figured it had to be a morph but I missed on the rest. Thanks for the help. I think Pat was real close because the mountain I was on is supposed to have a titanium deposit. I'll look for actual rutile next time I'm up there.
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Post by Chigoe on May 10, 2007 16:32:49 GMT -5
Looks like Rutile to me.  |
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Post by genchaos on May 13, 2007 19:19:41 GMT -5
These photos show some more of the specimens. If you look at the limonite photo gallery at mindat you can see why I agree with jbeckert.   |
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Post by jpolk123 on Jun 14, 2007 17:49:28 GMT -5
Looks like rutile to me.
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Post by genchaos on Jun 15, 2007 1:46:45 GMT -5
Someone give me some kind of test. What's the easiest way to determine that I have a titanium crystal here rather than iron? So far, two of the kind people I trade with have sent me limonite and the only difference I found was that my crystals were heavier and have better definition. I would LOVE for this to be rutile, but all the evidence, so far, is pointing toward limonite. Anyone can say it looks like rutile--who can show me how to prove it? Here are some photos of my most recent finds. Notice that hematite buds are mixed right in.    |
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Post by dr00bie on Jun 15, 2007 9:14:38 GMT -5
Correct me if I am wrong, but the mystery mineral looks to have a cubic crystal form... rutile has a tetragonal crystal form, and in my searches I was unable to find anything about cubic formed rutile.
I am thinking it is a limonite pseudomorph after pyrite...
Drew
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Post by genchaos on Jun 15, 2007 12:02:46 GMT -5
Thanks Drew. I agree because everyone who has voted limonite so far has had specific reasons and explanations. Those for rutile haven't offered any reason, support, test, etc. The one specimen of rutile I have is tetragonal and also has a silvery coloration rather than the brown-red of the stuff above.
I think the rutile votes are coming because of the first photo, which I agree is unusual. The cube has beveled edges on all complete sides. I have only found a couple like that and I have no explanation for it since I've never seen pyrite form that way, personally. Anyone?
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Post by JohnD on Jun 16, 2007 7:30:44 GMT -5
I find a lot of specimens that look a lot like yours in an area near Clemson, SC. Mine are goethite and they vary in specific gravity and hardness. When I break open the heavier ones they are mostly pyrite inside and the lightest ones break into what I assume is limonite.
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Post by Jbeckert on Jul 27, 2007 15:01:41 GMT -5
Nice extra photos!
I still vote for limonite! Did you find these in AZ or were they aquired some other way? I'm Curious, how big is the first photo in comparison to the rest?
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Post by Jbeckert on Jul 27, 2007 15:09:03 GMT -5
Also a lot of rutile that I've seen is a bit shinier than that like a more metalic sense, being titanium dioxide and all. If you really want to find out I can probably have an xrd done for you pretty quick if you want to send a bit my way.
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Post by colorshapetexture on Jul 27, 2007 22:12:57 GMT -5
if it is rutile it will streak red... try polishing a corner of one .. if it polishes like metal.. Rutile .... that looks more like a garnet
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Post by genchaos on Jul 28, 2007 19:52:53 GMT -5
The deposit is in a vein of andradite garnet and the cubes are found in veins of hematite and goethite. The vein is part of a geothermal vent, rather than a clastic dike. The material has opalized chalcedony running through it like melted glass. The first cube is about 1 1/4 inches. The others are 3/4 inch and smaller. Some of the cubes I've found show signs of morphing into garnet with a layered effect. Garnet is supposed to be very absorbent of surrounding metals. Some of the cubes, when cracked open, still have pyrite inside them, so I'm sure limonite is the proper ID, but because of the crazy combination of minerals and gems on that mountain, it's not possible to give them a blanket classification. Every place I've found them they seem a little different.
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