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Streak Test Question!


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Can someone please answer this for me? I have accumulated a nice little collection of meteorites from a local dry lake. I hear, and read, that a meteorite will not leave a streak on a piece of unglazed ceramic. Every one of the meteorites that I have leaves a brown streak on my sharpening stone when I first start to file a window in it. However, once the window is filed and I am actually making contact with the inside of the meteorite, it no longer streaks. So the question is: Should the streak test be done with a rough section of stone, or with the area where the window is filed? I know for sure that these are all meteorites as I have had several experienced hunters and collectors look at them, and they all agree they are authentic. So when I see someone who is questioning one of their finds being told to do a streak test, I worry that they may be throwing away something that could possibly be genuine because they are doing the test with a raw part of the stone, which will streak in order to remove the results of weathering.

All comments are welcome as I am just trying to learn more.

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My outlook is ALWAYS get to the interior of any sample before doing a streak test.
As you can imagine Chris the exterior has built up a coating from deterioration and also leaching of earth minerals from sitting on or in the dirt and the effects of weathering.
Some people don't like it when I say to newbies to carry an old file with you in the vehicle. That's a quick way to "see" the interior of any sample/suspect pieces.
I lay the file flat and stationery on the bed of the truck and rub the sample across it, that's the easiest and quickest procedure I have found.
Hapy Huntn Bud

Edited by frank c
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My outlook is ALWAYS get to the interior of any sample before doing a streak test.

As you can imagine Chris the exterior has built up a coating from deterioration and also leaching of earth minerals from sitting on or in the dirt and the effects of weathering.

Some people don't like it when I say to newbies to carry an old file with you in the vehicle. That's a quick way to "see" the interior of any sample/suspect pieces.

I lay the file flat and stationery on the bed of the truck and rub the sample across it, that's the easiest and quickest procedure I have found.

Hapy Huntn Bud

Hi Frank, thanks for the reply. I completely agree with your outlook, and I also carry a tool with me to file a window. I have a regular ole aluminum oxide whetrock (thanks to Mike Stang for that tip) that I use to file a window in them. I also carry a diamond sharpening stone with a 600 grit fine side for that smooth finish in the field. That method has worked perfectly so far. Then when I get home I use a 3000 grit sandpaper to put a nice polish on it. Hoping to find my first Gold Basin or Franconia meteorite after the first of the year. Will be hitting both places between Jan. and Mar. Maybe I'll find a little gold, too. Merry Xmas, Frank.

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Someone showed me one of the finds on Coyote. Wasn't a meteorite but another hunter told him it was. Be careful there!

You will get a streak if the meteorite is heavily oxidized. And yes, streak on a clean surface.

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I use a flat piece of oak about 5" long and 1" wide. I glued a couple pices of heavy "x backed" sandpaper to it. It weighs nothing and works great.

Streak does not have to be on ceramic or anything else. It is the color of the cuttings freed from the specimen. Any abrasive surface is good

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Someone showed me one of the finds on Coyote. Wasn't a meteorite but another hunter told him it was. Be careful there!

Jim, do you mind if I ask who this person is? Do they live in SoCal? I would like to try to get together with them to compare finds. It is easy to get some earth rocks out there confused with the real thing, but the meteorites just have a very definitive look, weight, and feel to them. Plus, all the bright nickel flakes in them are easy to spot with a good window. Thanks.

You will get a streak if the meteorite is heavily oxidized. And yes, streak on a clean surface.

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If you don't have a Plastic Toilet, the Lid makes a cool streak Stone. The under side is Unglazed and works good. I think I have a 20 year record on mine.

Homefire.....thanks for the tip. I used the tank lid a few times, then went to a thrift store and bought a coffee mug ( I don't drink the stuff ) and used it. But then I was given some really cool, portable, ceramic squares to carry in our packs by a very kind gentleman. Those are PERFECT. :thumbsupanim

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I am not at liberty to share names and I won't. I am just saying that some folks think they have meteorites and may not have meteorites and in this case, one from Coyote Dry Lake. Just because it's brown and is magnetic does not make it a meteorite.

Chris, be careful with the windows. Think about where you are placing a window with the entire process in mind. A window should be made with consideration as to where a cut might be made later on should you want to cut it for thin sectioning, etc. A lousy rounded window could lead to excess waste of material.

Jim

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So when I see someone who is questioning one of their finds being told to do a streak test, I worry that they may be throwing away something that could possibly be genuine because they are doing the test with a raw part of the stone, which will streak in order to remove the results of weathering.

Personally I do not like streak tests for meteorite ID. They became "popular" for meteorite ID because of the ability to differentiate between an iron meteorite (no streak/gray streak) and terrestrial iron oxides (red streaks), but given the varied compositions of stone meteorites a streak test doesn't really tell you anything, as all sorts of minerals leave different colored streaks and one could literally make a rainbow of streak colors using different meteorites. Visual ID is much more reliable for meteorites than a streak test is.

I also tell everyone to never throw anything out unless you're throwing it in your backyard, especially newcomers to the hobby. Better to have a pile of wrongs in your yard than to toss out what may be a 'rite to a more practiced set of eyes!

Edited by Mikestang
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