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Identity HelpSerpentine Mineral -- Any idea what this might be.

1st Jun 2012 00:00 UTCMark J. Sigouin

This orangish-brown mineral comes from the Penn-Maryland Quarry, Little Britain Township, Lancaster County, Pennsylvania. This quarry is literally just a high wall away from the Cedar Hill Quarry. It is a serpentine quarry providing fill, road chips, rip-rap.

I was wondering if anyone has experienced this mineral there and might know what it is.

I collected this myself about three or four years ago.

It is tabular. Ran as a short vein. Appears inter-bedded or laced with magnesite or hydromagnesite. It is soft. It has a waxy luster. Smaller pieces that broke off had a hexagonal look. What is left on these two specimens appear massive. Almost like a wax injected.

The orangish-brown mineral fluoresces a bright orange under longwave UV, less bright under shortwave UV.

The white minerals fluoresce bright white with traces of blue.

1st Jun 2012 01:02 UTCPaul Brandes 🌟 Manager

To me, it almost looks like brucite, but I don't believe brucite is fluorescent.

I'm sure someone more familiar with the area will chime in.

1st Jun 2012 02:19 UTCBen Grguric Expert

Mark, you can try this simple test. Take a tiny chip of the material and put it on a glass slide. Add a couple of drops of dilute hydrochloric acid. If it completely dissolves after several minutes with no bubbling it is likely to be brucite. If it dissolves with a small amount of bubbling and turns the solution greenish to brown it could be one of the hydrotalcite group minerals (e.g. pyroaurite, iowaite).

Cheers,

Ben.

1st Jun 2012 11:54 UTCMark J. Sigouin

Ben,

Would the muratic acid found at the hardware store be dilute enough, or should dilute it 2 or more times?

1st Jun 2012 11:57 UTCJosé Zendrera 🌟 Manager

... and if HCl disolves it with many bubbles and without turning to any color, could be just calcite.

Close to my house there is many calcite concretions that look similar and also they are fluorescent with bright orange color.

Greetings.

2nd Jun 2012 04:06 UTCRalph S Bottrill 🌟 Manager

Possibly saponite or a similar clay?

2nd Jun 2012 04:31 UTCMark Heintzelman 🌟 Expert

Likely it's Deweylite.

See Lizardite photo for Cedar Hill (same basic geological formation as you noted) here on mindat for reference.

That sample specimen I posted has this golden brown deweylite along with the deep olive green Lizardite.

MRH

PS Also note photo-350376 for this locale is NOT talc, but actually also dewelite, with nickel impurities which imparts that apple green coloration. (needs correcting).

3rd Jun 2012 11:01 UTCRalph S Bottrill 🌟 Manager

Deweylite is a mixture of stevensite and serpentine. Stevensite itself is of uncertain status, some may be saponite, some a talc-saponite mixed layer material. It all ready needs some XRD and chemical analysis to properly characterize it.

3rd Jun 2012 15:48 UTCVandall Thomas King Manager

I agree. This looks like classic deweylite, Whatever that is.

14th Jun 2012 02:40 UTCMark J. Sigouin

Ben,

I conducted your test. The two chips dissolved to a great extent in 1 molar HCl. There was only a slight efforvescence at first. The crystals became clear but retained a bright yellow brown color. The crystals became very tabular, but the edges were yet undefined. After about 10 minutes the solute turned lime green. After a day, it became roughly the same color as the crystals.

I believe the mineral is one of the hydrotalcite group minerals. Pyroaurite is identified as a mineral in the adjacent Cedar Hill Quarry though the one photograph of it is a green nickoline variety. The Wood's Chromite Mine, approximately one mile east lists pyroaurite and has photos. The color is about the same, as is the luster. My specimens are in general more massive.

At this point, I believe it is pyroaurite.

I agree that more work needs done. I will contact a friend that does SEm and XRD and see if I can get him to play with it a bit.

Thanks everybody.

14th Jun 2012 07:10 UTCBen Grguric Expert

Hi Mark,

1M HCl is about the right strength acid to use. Another simple test for Cl in the mineral structure is to dissolve the mineral in dilute nitric acid and then add a drop of silver nitrate solution. A dense white precipitate (AgCl) indicates a significant Cl content pointing to iowaite. If you dissolve in dilute nitric acid and then add a drop of barium chloride solution, a dense white ppt suggests sulphate, pointing to hydrotalcite.

But much better, your friend's XRD will tell you without a doubt if its hydrotalcite group, and SEM-EDAX will then help you constrain the species more precisely.

Cheers, Ben.

14th Jun 2012 12:09 UTCBen Grguric Expert

My mistake, in previous post. There is no sulphate in hydrotalcite, I mean't wermlandite or mountkeithite.

15th Jun 2012 23:35 UTCAnonymous User

Ime sure ive got a decent sixed piece from the gravel beds, ile post it tomorrow.

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