FMF - Friends of Minerals Forum, discussion and message board

[Pete Richards]

Here is a nice little rutile twin on {101}. It claims to be from Graves Mountain, but I question that attribution, and RutileFox agrees that it is suspect. Does anyone have an alternative locality to suggest? What observations support your suggestion, if you have one?

[kushmeja]

Could be from Chester County, Pennsylvania. Most of the PA rutiles have striations like yours, and similar twins occur there as well.

I have a lot of Grave Mountain rutiles & have a focus on them for my collection, and I would agree that it doesn't look like it is from there. Graves rutiles don't typically have striations like yours does, although I have seen a few with them, but only 1 or 2 ever with striations to the extent that your has.

[John Betts]

I doubt it is from Pa. which were found in farmer's fields and had abraded edges.

[kushmeja]

I would agree that most PA rutiles are pretty eroded for sure, but I have this one that is from Parkesburg that is quite sharp, and there are also pics on Mindat of a few with very sharp edges as well. Sorry for the poor pic, don't have my photo setup up.

[Pete Richards]

[John Betts]

If RutileFox does not know then who would?
He has the best rutile collection I am aware of...

[alfredo]

If I saw that piece without knowing what it was, I'd guess it was cassiterite rather than rutile, but I suppose that's just my Bolivian bias showing, and my absence of familiarity with rutile. (And being glued to a post like that makes it hard to check the density.)

[Bob Morgan]

The closest to your's appearance from this country that's on mindat is from California - both blocky and few striations.

[Pete Richards]

To John Betts: Yes, it's true.

To Alfredo: Yes, it's true. But I do think it's rutile. Right now I don't have access to the appropriate tools to check, sadly.

To Bob: Champion Mine? or elsewhere in California? I have thought about California as well.

Thanks to all!

[Bob Morgan]

Yes Champion

[alfredo]

Pete, I'm sure you're right about it being rutile versus cassiterite but, in case you ever need a method to test without having to unmount it from its stand, an electrician's meter should work. Rutile does not conduct electric current as far as I know, but cassiterite is a conductor, more or less, depending on the elemental impurities present.

[Pete Richards]

[alfredo]

A friend of mine is an avid hunter of gold with a metal detector and he was complaining to me that certain minerals caused him trouble because they sounded "hot" on the detector and caused him to perform sweaty work for nothing. Among the worst offenders were graphite, pyrrhotite, covellite, and galena. So that chat aroused my curiosity about what other minerals might conduct electrons, and why electrical properties are not, apparently, studied by mineralogists or included in new species descriptions. So I started testing everything in my collection at the time that was big enough to test, no micromounts. Of course just low grade qualitative study, nothing quantitative. Quantitative work would I guess be not very meaningful unless using standard sizes and shapes of specimen, resistance increasing with thickness, etc. Did get some interesting results, for example, sulphides with metallic luster (so not counting things like sphalerite, realgar, etc) are far better conductors than sulphosalts, so for a massive grey unidentifiable chunk, the conductivity will at least tell you whether you have a sulphide or sulphosalt.

The only mineral with non-metallic luster that I could find that conducted to some extent was my Bolivian cassiterites. Later I heard that there was a patent for coating automobile glass with thin transparent cassiterite films to conduct current to heat it for defrosting, without embedding wires in the glass. There is one other non-metallic mineral that allegedly conducts current, blue diamonds, which are naturally boron doped, but so far I haven't persuaded anyone to donate me a nice blue diamond for testing. ;((

Then there are the weird minerals that conduct protons instead of electrons, and those are not metallic at all, like vivianite, for example.

Apologies for wandering way off the rutile locality topic here.

[Peter Farquhar]

[rweaver]