From Italy

[saskrock]

My sister picked this up off the ground somewhere by Mt Vesuvius near Pompeii on her trip to Italy. She brought it back for my son. You would think she could have found one for here brother too . What the heck is it???

[traveler]

I would have to say some type of Obsidian, maybe Fire. When I was on the big Island of Hawaii, we saw some similar to that and if I remember correcrly it was on the top of a flow and looked like it cooled in a completely different way than the surrounding rock.

JUst my guess

[arappaho]

Not that traveler is too far off, I would guess some type of Scoria
rather than some type of obsidian.
If it's Scoria it should feel light for its' size.

[saskrock]

It is definantly light for its size.

[gemlover]

I'm not comfortable with either obsidian (glass) or scoria (usually very vesicular (holey)) for your sample, it has a definite metallic luster. Can a knife blade scratch it? Can a quartz crystal scratch it? Can your fingernail scratch it? What is its streak color?

Do you have the capability to determine a specific gravity for it?

Your sample has some resemblance to Sphalerite, but I need hardness and streak at least to rule others out.

[amythestguy]

It looks EXACTLY like a piece of good hematite that I bought. My guess is hematite. I am sitting here holding my piece of hematite and comparing it to the one on the screen and they look the same, almost perfectly identical. On mine the corners are a little sharper but thats probably because it was dug out of a mine and on this one since she picked it up off the ground so it weatherd a little which would make the corners and edges rounder.

[arappaho]

Gemlover, I for one am glad you aren't comfortable with either
obsidian or scoria. Thank you.
I guessed scoria because of its' cinder like appearance, but as
you noted, no vesicles.
The luster and abundant cleavage does make Sphalerite look like
a good candidate. Although in looking up Sphalerite it says the
name comes from the Greek word "sphaleros" meaning
'treacherous', which is an allusion to its similarity to other
minerals, making it hard to identify.
So roll up your sleeves, Saskrock. Seems your work is just
beginning. Scratch test and hardness are the easiest way to
start. (And you thought you only had one reason to beshrew
your sister. )

[saskrock]

I got the guess from someone on RTH that it might be a planted chunk of silicon carbide crystal today. So I did a scratch test and I think they might be right. It will scratch a chunk of quartz like it is butter (the quartz is scratched). Tried a streak test and got a scratch in the tile and nothing else. Whatever it is it is really hard. I scatter tumbled rocks I don't like quite as much around the local playgrounds so I can believe the planted therory. What do you all think???

[romare]

Synthetic silicon carbide (carborundum) will put it at about 9.25 hardness. To the best of my knowledge there is no natural silicon carbide larger than grain size. It certainly resembles carborundum.

It is way too hard for sphalerite if it scratches quartz. Does it scratch white? Can you do a specific gravity test?

[abuelito]

syntectic silicon carbide,i have some,formed in smoke stacks in foundrys,nice photo on midat,,some streets in moscow used as a filler,,use it for street fillers also in puebla,mexico,,,,ab

[saskrock]

I think it is synthetic romare, like you say it doesn't form naturaly like that and its way to hard to be anything else I know of and look like that. By scratch white do you mean the quartz? If so yes. If you mean this thing then I don't know as I am unable to scratch it. The wife won't let me use her engagement ring to try scratching it so I'm out of luck. I don't have a scale sensitive enough to test SG on something that light either. It is fairly light for its size though if it helps.

[gemlover]

looks like we have gotten to the bitter end. and another good lesson as to why you don't identify rocks and minerals just by looking at a picture, although the image does help.

[saskrock]

Yeah but without everyones best guesses I still wouldn't know what it was. Might not nail it from a picture but it definantly gives you a place to start testing. If nothing else I learned a lot about other rocks too. Nothing wrong with that.

[amythestguy]

What do you think, pretty close?

[xtldggr]

I have to Agree with Arapohoe and Gemlover I really dont think that the specimen posted was either scoria or obsidain as both are extrusive rocks, subjected to rapid cooling and therefore non condusive to the formation of large crystals as the specimen posted clearly displays. I would agree with Romare that the specimen appears to be silcon carbide/carborundum, a man made abbrasive. I have include a photo of carborundum for comparison.




-xtldggr-

[gsellis]

That looks a lot like a bismuth crystal I used to have. Made in a lab in Germany. Hey Amethystguy! Been to Italy with those holey pockets of yours?

[amythestguy]

Hey george I have actually been to italy and to pompeii itself but I didn't get to go on the slopes of the volcano. As for the bismuth I have some from a lab in Germany but it looks like this...


*mins. NOT wet

[saskrock]

It has to be silicon carbide. Being able to scratch quartz and agate as easily as it does pretty much rules out everything else as being way too soft. There are a lot of look alikes for this one though.

[arappaho]

Yeah, I was thinking abuelito pretty much nailed this one.