What mineral made these square marks?

Down in Copper Basin Wash in Skull Valley, these quartz pieces show up regularly. Can anybody provide an answer as to what made the square holes in this specimen? The biggest hole is about 1" square. Thanx!



Edited 1 time(s). Last edit at 03/18/2009 06:06PM by Paul Prescottstyle.

Looks similar to casts after anhydrite found in the NJ basalts. I don't know if there was anhydrite in the area where these are from though...

Bryan

Fluorite?

In bull quartz with some brown staining on a few of the cast edges, I would suspect pyrite.

Bill Besse

Pyrite would be with striation.
Too cubic for anhydrite.
Fluorite or halite?

Dear Paul;
WHICH Skull Valley in WHICH copper Basin? you wouldn't BELIEVE how many popped up! need a state. The little bits of rust mean little, that lack of striation imprints MIGHT! I'm thinking flourite was there, bcs pyrite, chalcopyrite, or ferroan dolomite are frequently associated on them.
Your friend, Steve

Not to be difficult but all pyrite crystals do not have striations, look at the famous Spanish pyrite cubes, not a striation between them.

Steven, sorry for the brevity of the locale description. Copper Basin Wash is in Skull Valley, Arizona. Prescott is about 20 miles east of here.
I've seen alot of pyrite in veins, and I've collected some Quartz and Calcite crystals in the immediate area. Thanx for your help. Paul

Hello,

I say fluorite. I have collected lots of that stuff in Southern Germany and my specimen look exactly like the one at your pictures.

Pyrite would give a lot of iron if weathered out, which will lead to a yellow to brown limonite staining on the specimen almost every time.

Attached a photo from one of these specimens

Regards,
Sebastian Möller

Thanks Sebastian, Now I would like to find some fluorite at this locale!

Dear Albert;
You are most certainly correct, not all pyrites have striations & the Spanish & Peruvian ones came to my mind, immediately; however, look anywhere, for unstriated cubes & you'll find them a much rarer bird (not counting small ones). The fact that quartzes are larger & most likely from some sort of ore development, makes it unlikely they'd be unstriated (unmodified by pyritohedral growth).
To Paul: YES, I'd be looking for where that came from! I'd be check ing the ground for more signs & every outcrop, along the way of any possible waterflow pattern! Check downstream (hill), as well as up; if there's more downetc., it means where you found that, is likely VERY close to where it came from. If there's nothing upetc.you are probably EXTREMELY close; it mean also mean you have to dig a ways, to reach the vein. GOOD LUCK!
Your friend, Steve

Hi Paul,

I think the cubic mineral was most likely fluorite. Very similar quartz/fluorite overgrowths, with the fluorite having dissolved away, are found in some of the mines in east Cornwall, England. See the attached photos showing the top and bottom of a large Cornish quartz specimen from my collection. On the bottom views, you can see cubic cavities where the fluorite used to be. Sebastian's photo of the German specimen is an excellent example, too.

Woody Thompson



Edited 4 time(s). Last edit at 03/19/2009 11:52AM by Woodrow Thompson.

Much of the fluorite to the East of you near the New Mexico border have and overgrowth of Quartz. Nearly all if not all of the great purple octahedron specimens have been etched out of quartz.

I suggest that you take an inverted cast of the indentations, or parts thereof, and try and look at the overall structure - you may be surprised at the end result.
If you are unable to take a plaster cast try a little "cling wrap" type material and place this over the specimen and then press in some plasticine / tac or clay of some kind, and see if you can get a better "impression" so that you can more readily see what the cast may be. I have found that this has clearly shown Fluorite as the dissolved material - particularly if the imprtession is cubic, dodecahedron, trapezohedron etc.

I strongly suggest fluorite - in fact that is usually my first guess when Quartz is involved.

Now I am not a geologist or mineralogist etc but from experience it often appears that in the overall formation of minerals, some Fluorine seems to "come and go" - ie it crystallises and then is simply dissolved away after it has been covered - usually by Quartz. I don't know why but this is something that seems to happens. It is as if some other material initially covers the Fluorite ( there is often a band of material between the Quartz and the material that was dissolved, the Quartz is formed and then the Fluorite is dissolved away.

I am sure that there are many mineralogosits/geologists out there that can explain this phenomenen (not sure if I spelt that correctly!) in more technical terms.

I am always fascinated that that Quartz can be dissloved away from Fluorite - albeit generally leaving a dull or matt finnish with Hydrofluoric acid - ie fluorine is involved and yet the Fluorite itself also can be dissolved, probably through some hydrothermic reaction involving H2SO4. Don't think I would like to be in either of these solutions !

Hope that helps (hope I'm right!)

Here is a plate I collected near Bisbee It is I think similar to your piece. There are some bits of flourite left in places. Some pieces will have the cubes of flourite still in place with quartz crystals radiating out from them. Dave

These hollows are what the geologists call 'box works', they are very useful in geological prospection, as they are a sign of the existance of metalic (Fe) minerals, usually pyrite and other sulfides, near earth's surface.

The atmosphere's oxigen reacts (oxidize) the iron ions, but before they desappear, they get 'rusty' and leave brownish marks on the quartz surface, as it seems to happen in your photos.


Jorge

Hello,

Here are some pics of the back side of a quartz specimen (the other side has xls up to 2 cm) I have found at Todtnau, Black Forest, Germany last May, showing fluorite negatives in quartz. On the third one you see a rest of a fluorite cube sticking in It's cavity. The red line indicates the dimension of the hole, the green one the actual size of the xl.

Regards,
Sebastian Möller

Well no Fluorite was found on our return hike through the area. But a few new quartz crystals turned up!

Looks similar to casts after anhydrite found in the NJ basalts. I don't know if there was anhydrite in the area where these are from though...

Bryan ............i agree bryan ive seen these type casts in the nj balsalts as well....

Paul, have you tried to measure any of the internal angles on the casts? Making a positive with clay would help with that. Everyone is assuming the casts are from fluorite or another isometric mineral. That may be, but if the angles are not 90 degrees, I would suggest looking at calcite as the mineral that disolved. I have carnelian from Green Brook in Berkley Heights, NJ showing similar impressions, and also some quartz from Montgomery Co., AR that shows the impressions of calcite crystals on the bottom of a quartz plate. They are definitely not anhydrite, which makes long thin cavities when it dissolves.