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Shiny metallic rock


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#1 benesound

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Posted 05 December 2006 - 03:44 AM

I found this interesting rock, partially buried in a large hole, in the backyard of my house years ago when I first moved in.

It's approximately 6" tall and weighs just under 10 pounds.

It's shiny, very hard, doesn't rust, and a magnet isn't attracted to it.



The top, or bottom(depending on how you look at it) is smoother than the sides. It almost looks like it had been melted.



I broke three hack saw blades attempting to cut a small piece off.



Any thoughts as to what it could be, or where I could find out?

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#2 Mark

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Posted 05 December 2006 - 03:54 AM

Mark: Do you live near a college?  Geology professors will quickly identify the rock. It looks like some sort of ore, but it's shiney like it has nickel in it. Interesting looking specimen for sure. Breaking hacksaw blades on it actually helps determine it's hardness, which helps in the identification process (I'm thinkin' back to my 7th grade geology class...heehee)
Approximately where do you live...that may help identify it.

Edited by Mark, 05 December 2006 - 03:55 AM.

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#3 Kosh

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Posted 05 December 2006 - 09:40 AM

Looks like Aluminum that has seen some serious heat. Anything ever burn down on that site?
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#4 benesound

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Posted 05 December 2006 - 11:34 AM

I have some experience with recycled (melted) aluminum, and this is too heavy and hard to be aluminum.

#5 D.Rabbit

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Posted 05 December 2006 - 02:22 PM

I'm a bit of a rock hound.
It looks like Specularite Iron Ore

One would think iron ore should be attracted to a magnet, my specimen isn't either.
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#6 Orpheus

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Posted 05 December 2006 - 11:40 PM

Tes, I'd agree with D. that it is probably some form of hematite (specularite is one form, but my sample happened to look more like this. You can imagine how excited I was to find that at 6 or 7)

You can tentatively identify it at home by rubbing across a piece of hard unglazed ceramic (the rough surface of a mortar&pestle will do, as will the back side of some bathroom tiles. Many other similarly textured surfaces are too soft, but hey, it can't hurt) Since hematites are basically iron oxides, if you see a reddish rust streak , it's probably hematite or a similar iron mineral. Other minerals may have other colors/tinges

Another easy measurement to do at home is specific gravity: weigh the rock then fill a container with water to the very edge, then lower the rock in and measure the overflow to determine the rock's volume (the old Eureka! trick) weigh/volume = sp. gr.

If you can make out any crystal or cleavage structure, that's useful info, too.

Since the rock is so dark and shiny, you might want to use indirect primary and secondary ("fill") lighting to bring out colors structures and details. Also try illuminating at an angle, instead fof "head-on" to the camera. Sunlight is a good primary source, but instead of the high contrast of direct sun, try going tover yto the shaded side of the house and photographing it by the light of the bright sky. A couple of pads of white paper should make good "fill light" sources. Since I know you're a creative type, you might find the  whole thing an artsy challenge. Dull silvery materials, like old aluminum cookie sheets or big pots can also be low-glare fill light reflectors

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#7 benesound

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Posted 06 December 2006 - 12:34 AM

Thanks D, and Orpheus.

I'll see what other information I can come up with and attempt to take some better pictures.

One question, when you said to measure the overflow, do you mean weigh it? I want to make sure I do this right.

#8 Orpheus

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Posted 06 December 2006 - 03:10 AM

It depends what tools you have available. Either the volume OR weight of the overflow will will do. A lot of dieters or frequent mailers have scales that measure to the nearest gram or even 1/10th gram. Many hobbies like photography, plastic casting and ceramics use graduated cylinders. I'd hope every kitchen has a decent measuring cup or set of measuring spoons.  

If you don't have an accurate weight scale, you can make an acceptable balance scale from string and a yardstick or ruler, and weigh the rock against measured amounts of water from a measuring cup--just be aware that 1 ounce of water by weight is .96 fluid ounces by volume (And yes,  you would *not* have wanted to to play "drip stuff in the toilet and flush" with Toddler Orph. The girl next door always got bored and demanded to play "Doctor" instead.)

Since you are looking at a roughly 10 lb (4.5 kg) rock, with a volume of  17-30 fl oz (0.5- 9L)  and  0.2 g/cc is plenty of accuracy for a mixed mineral sample, "the nearest ounce of weight and the nearest fluid ounce' will be good enough. Of course, if you WANT to do fractions of an ounce and teaspoons, I'll cheer. I'll even give you a trick for improving the resolution of a yardstick balance-scale by varying the distance from the weights to the fulcrum--and if you're *really* accurate, I may give you the phone # of the little girl girl next door. I hear she just got a divorce. The last time I saw her she was the spitting image of Elizabeth Montgomery

#9 Christopher

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Posted 06 December 2006 - 11:28 AM

View Postbenesound, on Dec 6 2006, 12:34 AM, said:

One question, when you said to measure the overflow, do you mean weigh it? I want to make sure I do this right.

You get the weight (mass, essentially) of the rock from weighing it on the scale.  The displacement test is to calculate its volume, and dividing mass by volume will give you its density, which is key to determining what material it is.  So you want to measure the volume of the water that spills.

However, the density of water is known (one gram per cubic centimeter), so you could calculate the volume of displaced water by weighing it.  But it's simpler just to measure the volume directly.  If you have a graduated container large enough to hold the rock, then you can measure the amount of water spilled out just by seeing how much the level has dropped once you remove the rock.  (Although in that case, you'd have to pull it out with a string or something so your hand didn't displace extra water when you pulled it out.)

I suppose the ideal way would be to place a container large enough to hold the rock inside a large empty mixing bowl or something similar (with a flat enough bottom for the container to be level), fill the container to the brim with water, gently lower in the rock, then remove the container and the rock carefully to avoid spilling any more water (maybe put a cover over it once the rock is inside), and then pour the spilled water in the mixing bowl into a large measuring cup to measure its volume.  That will equal the volume of the rock.

Edited by Christopher, 06 December 2006 - 11:29 AM.

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#10 Rhys

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Posted 06 December 2006 - 12:55 PM

... or, you could measure the level before you put the rock in, then compare it to the level after you add the rock.

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#11 Christopher

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Posted 06 December 2006 - 01:11 PM

^^Well, yeah, if you want to do it the easy way. ;)  And if you have a large enough graduated container.

Edited by Christopher, 06 December 2006 - 01:11 PM.

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#12 benesound

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Posted 06 December 2006 - 04:23 PM

Actual weight of the rock/mineral is 9.5 pounds

Volume (Water Displacement)  is 1.4 pounds

Density (Specific Gravity)  is 6.78

This could put it in the same category as galena, hematite, magnetite, nickel-iron, and pyrite.

Edited by benesound, 06 December 2006 - 04:23 PM.


#13 Christopher

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Posted 06 December 2006 - 04:46 PM

View Postbenesound, on Dec 6 2006, 04:23 PM, said:

Actual weight of the rock/mineral is 9.5 pounds

Volume (Water Displacement)  is 1.4 pounds

Density (Specific Gravity)  is 6.78

This could put it in the same category as galena, hematite, magnetite, nickel-iron, and pyrite.

Err, what?  Pounds aren't a unit of volume.  You have to divide the weight (mass) of the rock by the volume of the water.  Density isn't a dimensionless number; the units matter.

Let's see...
9.5 lb = 4.31 kg
Volume of 1.4 lb of water = 1.4 pints = 663 cc
Density of rock = 4310 g/663 cc = 6.5 g/cc = 6500 kg/m^3

Edited by Christopher, 06 December 2006 - 04:51 PM.

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#14 Orpheus

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Posted 06 December 2006 - 06:09 PM

I dunno, working with higher precision conversion factors (unwarranted, I know, given the rules of accuracy and precision), his final figure is spot on in g/cc, the preferred unit in minerology), so rather than ragging on him or not showing his work, I'd give him mad props for getting it right.

Of the candidates he lists:

Pyrite (fool's gold) is generally a brassy gold (but has a black streak test)
Galena (used in in crystal radios) is a SOFT lead sulfide, and will mark paper. It's usually >7 g/cc
Nickel-iron will attract a magnet.

If it's not some hematite (reddish streak test), it could be a member of the columbite/tantalite group.

There are a few other candidates, but I'd like to hear the results of the streak test before working up a differential. Another surface that will work for the streak test is the bottom rim of many inexpensive household ceramic dishes or mugs, which are often partially unglazed or rough due to issues during firing, and household wear.

Edited by Orpheus, 06 December 2006 - 06:10 PM.


#15 Christopher

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Posted 06 December 2006 - 07:40 PM

View PostOrpheus, on Dec 6 2006, 06:09 PM, said:

I dunno, working with higher precision conversion factors (unwarranted, I know, given the rules of accuracy and precision), his final figure is spot on in g/cc, the preferred unit in minerology), so rather than ragging on him or not showing his work, I'd give him mad props for getting it right.

I thought I was using very precise conversion factors.  I even checked it against an online conversion calculator that gave its conversion factors to something like eight figures.  The only thing I rounded was the volume, which was closer to 662.5 ml rather than 663.

Also, if the numbers had been different, would the result have been as accurate?  I mean, what he ended up with there was just the ratio of the rock's weight to the displaced water's weight, a dimensionless number.  Isn't it just coincidence that it corresponds to the density in g/cc?  After all, a number isn't useful unless you can compare it to something meaningfully, and then you have to know it's the right number.

My thinking is, if he wants to use this technique with other things in the future, or if others reading this thread want to do their own experiments, they need to know the right way to do it so they'll get consistent results.  I don't think one lucky accident is anything to be praised, not if it doesn't help people in other situations.  It's the teach-a-man-to-fish principle.  Filling in the right answer on one test isn't what's important; understanding the principles so you can apply them generally is.

Besides, I wasn't just "ragging," I was confused.  I didn't understand the meaning of the results as presented, so I did my own calculations to get an answer I could understand.

Edited by Christopher, 06 December 2006 - 07:41 PM.

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#16 benesound

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Posted 06 December 2006 - 11:11 PM

Completed the streak test.

Streak is a shiny silvery gray color.

Edited by benesound, 06 December 2006 - 11:16 PM.


#17 Mark

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Posted 06 December 2006 - 11:16 PM

View Postbenesound, on Dec 6 2006, 10:11 PM, said:

Completed the streak test.

Streak is a silvery gray color.

Mark: (with rough voice and southern accent)  
You got yerself a piece o' Kryptonite, boy! :nod:

Edited by Mark, 06 December 2006 - 11:17 PM.

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#18 benesound

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Posted 07 December 2006 - 12:23 AM

View PostMark, on Dec 6 2006, 11:16 PM, said:

View Postbenesound, on Dec 6 2006, 10:11 PM, said:

Completed the streak test.

Streak is a silvery gray color.

Mark: (with rough voice and southern accent)
You got yerself a piece o' Kryptonite, boy! :nod:





Good thing I'm not Superman. :D



Wait a minute,... I thought Kryptonite was green. :blink:

#19 benesound

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Posted 07 December 2006 - 12:28 AM

"Specific Gravity: Specific gravity (SG) is a measure of how dense a mineral is. It compares the mass of one gram of the mineral to the mass of one gram of water. So, a mineral with a SG of 4.5 is 4.5 times as heavy as water. "

Maybe I done something wrong.

I thought if I weighed the displaced water and divided that into the weight of the rock/mineral, that would give the SG.

#20 Orpheus

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Posted 07 December 2006 - 03:16 AM

You're absolutely right: in geology, another term for "specific gravity" is "relative density" (understood to be "relative to" water) and the method you describe was standard for working geologists well into the 20th century.

Christopher, I believe that your slight discrepancy is due to an inaccurate implicit conversion (pound = pint, fl oz = oz.). It's even a common saying: "a pint's a pound the world around" but I'm sure you noted the discrepancy when you did the metric system in grade school:

1 US fluid ounce = 29.5735297 ml
1 oz avoirdupois = 28.3495231 grams
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Therefore a fluid ounce of water (1 g/ml) can't weigh one ounce. There's no reason it should. Water has no special role in avoirdupois, developed for commerce, and the more commercially important wines and spirits have a lower density than water (Indeed, calculating the density of ethanol/water mixtures is a common problem with surprisingly broad applications. I've often seen utilities for calculating it [e.g.])

So remember kiddies: "a pint's a bit under 0.96 lb the whole world round -- at 20 C, 1 atm pressure"
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Consider that the purpose of the immersion is to make both volumes identical. Therefore it will always cancel out!

Had you converted the measurements, as given, to metric, without implicit conversions, you'd have gotten something like 4309 g/635 g = 6.78. Converting to grams then ml (1.4lbs * 454 g/lb = 635.6 g = 635.6 ml of water) gives the same answer (6.779) to within the limits of our approximation of water's density (actually 0.99820 g/ml at 20C, 1 atm)

I hope you don't think I'm picking on you. I thought you'd find it interesting. You re quite correct that Benesound seems to have labeled his results "volume" in a generic linguistic abbreviation (weight of the volume of water) and not the proper physics/math sense. You *know* how confused *I* get when SF uses terms colloquially rather than strictly.

But back to the problem at hand:

Benesound, that's one interesting rock, and I have found quite a few less common minerals it could be, but frankly, I got distracted half a dozen times as I wrote this, so I have to head to bed. I do have a few questions now (and more later)

1) are you sure you got a proper streak? E.g. sometimes a mineral will powder the streak plate (a "real" streak plate has a hardness of 6-6.5, but with  household ceramics, who knows?) or sometimes you get a flake of another mineral (e.g. mica, which looks like it may be present in that sample, has a silvery streak)

2) do you have a nice chunk of quartz you can use to test its hardness? (Scratch test) can the rock scratch a piece of iron or steel?

3) can you describe it to us. We have the pictures, and that's great, but an you describe anything that might not be immediately clear to someone who is only looking at the picture, without every having seen the actual rock? How would you describe the exact shade? is it brownish? bluish? Greyish?

4) can you describe the brownish parts of the mineral? general density, texture, adherence to the blacker rock, etc.

5) can you crack/fracture/cleave a small fragment with a hammer (tap, don't smash) do you see cleavage planes or crystal-like surfaces? Can you describe the fracture surface, if it is not crystalline?

I'm sure I'll have more annoying questions later. maybe you'll be lucky and it will be treasureite or something (with a name like that, it's got to be good Frankly, I'm hoping for an unknown alien alloy (the great thing about a *truly unknown* alien alloys is the look on their face when you patent them -- they didn't even know it existed on their scavenged hulls, and already they owe you royalties. Of course, if they get all testy and warlike about it, it just sucks all the fun out of it.)




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