Arsenopyrite and zinc come to mind, but let's not get ahead of ourselves,
and make sure we get a good fit for that remarkable conchoidal fracturing.
As usual with this sort of specimen, the initial question is mineral or metal?
We'll get to that.
- density? (use water displacement method)
- magnetism: attracts steel?, attracts a magnet?
- hardness? (try penknife, glass or anything to-hand as commonly referenced for Mohs scale)
- anything else
Rock found on a friend's driveway here in London among other common pebbles that covered the drive.
Has no atraction to magnets or metals
can not scratch with a penknife
Weight in all 19 grams
Used to be a one item before I smashed it with a hammer and broke like glass
There is no particular smell
Scratches glass very easily.
Size check photo.
Could not do density no measured jar.
Thanks for the info.
Candidates, going on Hardness: 5.5-7.5, and other info above, but ignoring the origin in your drive gravel:
- Chromium - http://webmineral.com/data/Chromium.shtml (fracture OK)
- Sperrylite - http://webmineral.com/data/Sperrylite.shtml (fracture OK)
- Skutterudite - http://webmineral.com/data/Skutterudite.shtml (fracture OK)
- Fersilicite - http://webmineral.com/data/Fersilicite.shtml (fracture OK, but too rare)
- Ruthenium - http://webmineral.com/data/Ruthenium.shtml (fracture unsure)
Rejected becuse of rarity, habit (eg. occurs only as granular masses or disseminated), etc.:
- Iridium - http://webmineral.com/data/Iridium.shtml (no - squashes under hammer rather than breaking)
- Cobaltite - http://webmineral.com/data/Cobaltite.shtml (fracture OK)
- Isomertieite - http://webmineral.com/data/Isomertieite.shtml (fracture may be wrong)
- Oenite - http://webmineral.com/data/Oenite.shtml (fracture not quite right)
- Gudmundite - http://webmineral.com/data/Gudmundite.shtml (fracture not quite right)
- Rammelsbergite - http://webmineral.com/data/Rammelsbergite.shtml (fracture not quite right)
- Pararammelsbergite - http://webmineral.com/data/Pararammelsbergite.shtml (but fracture wrong)
- Haxonite - http://webmineral.com/data/Haxonite.shtml (fracture unsure)
- Jolliffeite - http://webmineral.com/data/Jolliffeite.shtml (fracture unsure)
- Ferroskutterudite - http://webmineral.com/data/Ferroskutterudite.shtml (fracture unsure)
- Hongshiite - http://webmineral.com/data/Hongshiite.shtml (only microscopic crystals, hence fracture n/a)
- Yixunite - http://webmineral.com/data/Yixunite.shtml (wrong in various aspects)
- Rutheniridosmine - http://webmineral.com/data/Rutheniridosmine.shtml (wrong in various aspects)
...So I really could do with that density data...!
Streak, would also be useful...
I mis-read your statement about scratching glass. The hardness is probably more than 7 (the hardness of glass actually varies a lot depending on the type of glass; Gorilla glass is almost 9).
So ignore the candidates I listed above.
Being able to scratch it with sandpaper suggests a hardness of less than 7-9 (7 if quartz sand, 9 if carborundum).
So I think we can say the hardness is in the 7-9 range on the Mohs scale.
That would fit with chromium, which also has a conchoidal fracture.
It would be very unusual to find a piece of native chromium as large as yours, so I suspect it would have come from an industrial plant of some sort, eg. a chrome-plating factory.
- The bronze colour... That could be its real colour; that may oxidize to the 'silver'/yellow-'gold' colour we see.
Alternatively, the bronze-ness could be due to remnant dust from the sandpaper. So best to ignore the bronzeness as it could be misleading.
- You say it is yellow?!... I see the colour as 'silver' in the photos. Is that yelllow/'gold' the streak colour?
Please clarify that. Re streak test, see http://geology.about.com/od/mineral_ident/ig/streak/
- Density... If it is 3.8g/ml is it not chromium. The only metal or metallic mineral that fits with approximately that density and a hardness around 7 is hibonite, which is black - so something's not right. Please could you check your denisty measurements/calculations...
If you can tell me the streak colour (as per link above) and check the density, we have a good chance of making a reasonable determination ourselves. If we find that nothing fits the data, you could send it somewhere for analysis. No point sending it to me, I'm afraid. Although I'm uni trained as a geologist, I don't have access to a lab these days. You'd need to find a lab with suitable equipment such as a mass spectrometer or an electron microprobe. Maybe you have a university with an earth science / geology dept. nearby? If so, there's a good chance they'd be able to find somebody to make a comment, and possibly guide you onwards in your quest, eg. to somewhere with suitable equipment. There's a good chance, however, that you'd be charged for the analysis. You could also try a local geology club as a starting point.