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Is this a rough sapphire rock? Thank you for answers


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I'm assuming your are referring to the whole sample in the photos; hard to say just from a photo, but if you take a piece of quartz and draw it across the sample, where the sample is flat and smooth and feel the quartz "bite" into the sample and/or leave a scratch then the answer is no, the sample is not sapphire or corundum, the name of the non-precious form of sapphire.

There is a scale of hardness called the Mohs Hardness Scale that geologist & mineral collectors use to help ID minerals. Quartz on this hardness scale has a value of 6 and sapphire/corundum has a value of 8 so, quartz cannot scratch sapphire/corundum but sapphire/corundum can scratch quartz. Also, quartz will not scratch another piece of quartz. When doing the hardness test, use a piece of quartz with a sharp edge or point.

Let us know the results of your hardness test.

Here is the Wikipedia link to the Mohs harness scale:

https://en.wikipedia.org/wiki/Mohs_scale_of_mineral_hardness

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Well the sample's hardness is either equal to or greater than the hardness of quartz (6). That's good information. If you have a tungsten carbide hole starter or cutting bit (hardness of 9) lying around, or go to Harbor Freight and purchase one, then try to scratch the sample with the tool. If the tool does not scratch the sample then it is corundum. To be honest, the sample looks very much like a piece of blue-gray, quartz I have in my mineral drawer. Keep us informed.

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Might be, but on one that rough, I need to see it turned in the light to catch the glint of any flat (stair step) faces, it's kind of hard to describe, but if you posted a video of it rotating in sunlight what would probably be enough. If it is, the quality is low enough that it is really just a piece of corundum, still interesting though.

Edited by bigrex
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If the cutting bit is tungsten carbide then it looks like you have some corundum. Like bigtex asked, a video of the sample, made under sunlight, would be the "nail in the coffin" if it showed the reflective "stair step" partings.

Can you tell us the general area where the sample came from without disclosing the find location? That would also help with the IDing the sample.

I have not seen corundum samples in the field, just lab specimens, so this is a fun, learning exercise for me.

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Unitedstatesofamerica1, I had a look at your video & I did not see the flashing of light off any partings I would expect for corrundum, but the sample is well worn & rounded so the partings may have been smoothed off. Can you tell us approx where the sample came from? maybe to within a 7 mile area. This way we can look and see if the geology of the area is right for corrundum formation. If the area's geolgy is of limestone or basalt then there is no way it is corrundum. Let's see what bigtex observed.

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I also took a look, It's hard to tell, but I can't see any flat reflective areas. There is maybe some possibility it still is corundum. Here is a video that displays very well what I was looking for as far as the shine aspect...I also agree with 4meter, if you have sedimentary rocks around, that is not a good sign. It would be a good sign if you have metamorphic rocks in the vicinity such as mica schist, phyllite, marble, gneiss, etc.

Edited by bigrex
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bigrex: wow! that is big hunk of corrundum! Look at all the partings. I'm envious.

unitedstatesofamerica1: There are some areas in the very eastern portion of the Lehigh Co that have the right geology. These areas have precambrian felsic gniess rocks with mafic gniess rocks, or old basalt (mafic) and granites (granites) that have been converted into metamorphic rocks. The geology is favorable to corrundum. A quick Google search for Corrundum\Pennsylvania came up with specimans of corrundum from Lehigh Co. (link:http://www.johnbetts-fineminerals.com/jhbnyc/mineralmuseum/picshow.php?id=50255). Looks very favorable that you have a corrundum specimen; nice find. :yesss:

The USGS has geologic maps of all the States; they give a general overview of the geologic settings of each State with the type of rock and age if known. Comes in very handy. Here is the link: http://mrdata.usgs.gov/geology/state/

Spell check keeps changing corrundum into corundum on this machine. I need a geologicly trained computer. :)

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Great researching 4meter, and I am impressed that the specimen on johnbetts does resemble Unitedstatesofamerica1's find...That is a big fat corundum lump in the video, it was not my own clip, but I just was lucky to find one that did a good job of illustrating was I was attempting to describe.

Edited by bigrex
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