Newbie rock hound needs your expertise

[ugunaeatthat?]

Hello treasure hunters,

I'm new to rock hounding and have several pieces that I brought home even though I know next to nothing about each of them. I am supposed to be out there using my metal detector but keep getting sidetracked with the cool looking rocks in my path.
Here are 2 that I'm most curious about and I'm going to post several others shortly. I have never seen that color of blue in a rock before and am wondering how it came to be, also are those quartz crystals?
In the other rock it looks like elongated crystals kinda swirling around? I have never found another rock even close to this one and am hoping for some help identifying it.
Any info at all would be a huge help and much appreciated.
Thanks you guys.

 

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[woof!]

One on left is a shell fossil conglomerate. If you post the pic in the fossils forum and say where you found it maybe an expert can tell you more about it, for example what geological era it's from.

Ones on right, blues are most commonly associated with copper ores, so if it's a known copper mining region it's probably some kind of copper ore. In any case, someone here who's a well informed rockhound can probably give you a positive ID on it based on its very distinctive color and mottled appearance. .......Also, in the photo it looks like maybe the blue is a hard mineral coating on a rock of other composition: have you broken or chipped any of these to see if they're like that all the way through, or if the blue is only a coating? That might make a big difference in identification.

I've seen that color in a few rocks in arroyos in the Franklin Mountains near here (El Paso) but don't recall their surface appearance. The rocks here with that color I suspect the color comes from small amounts of copper, which is present in the Franklins but not in mineable concentrations. In some areas in the Franklins we also have shell fossil conglomerates just like the one you showed a pic of.

(hmm, don't laugh...) any chance those are rocks which were painted blue for some artistic purpose, and after they'd served their purpose they got dumped and the paint is in the process of disintegrating?

--Dave J.

 

[ugunaeatthat?]

Trust me bro I'm not laughing. If you only knew how many times I picked up a rock that looked really neat on the ground to get a closer look, just to find out it was a painted rock!
So I just went to the gagrage and chipped a piece away. It's much darker inside but it does appear that the blue runs through and through. As for copper mines in the area, I can't say for sure but I have heard of several Tin mines close by. Does the inside of this rock look like regular old granite to you?
Thanks by the way for the reply, I do appreciate it.

 

[woof!]

I've seen stuff like that in the Franklins (El Paso, TX), and there are old abandoned tin mines in the Franklins. Pretty sure both the blue stuff and the tin ore are associated with hydrothermal alteration of rhyolite. However there is also granite there and maybe it's in the granite, it's been a while since I was there.

--Dave J.

 

[ugunaeatthat?]

Well Met Dave,

I will take your information and begin researching. I appreciate the time you took looking into this and your replies.
Happy 4th!

P.S. I gotta know, "BS detector" Real or just being clever? Either way thats good stuff

Kelly

 

[woof!]

I got it figured out very early in life that if I didn't keep my BS detector turned on and tuned up, I was going to grow up as gullible as the adults around me. Which was not fate I wished upon myself.

--Dave J.

 

[woof!]

The photo of the chip appears to have zones which are jet black and crystalline. If this is correct, check the resistance with an ohmmeter. If it's conductive it's likely either galena or tin (cassiterite). And if so, check with a magnifying glass. Galena has distinctly cubic crystal structure, whereas cassiterite does not. If the black stuff is nonconductive, but jet black and crystalline, it's probably magnetite and will be pulled to a magnet. If not pulled to a magnet, possibly specular hematite or limonite but the association with blue makes that unlikely.

The yellow-brown zones are stained with goethite (ferric oxide hydrate). It's produced by the weathering of iron minerals in the rock, that's why you see it on the outside but not on the inside. Lots of that around the Franklin tin mines, too.

The more I look at those rock pix, the more I want to go hiking up to the Franklin tin mine and see if I can find a rock just like yours, just for the heck of it.

--Dave J.

 

[ugunaeatthat?]

Awesome stuff Dave,

You've given me several tasks to complete for which I am grateful. To be honest I'm not sure I even own a ohmmeter or if i do how to use it correctly. My girlfriend is more knowledgable when it comes to such things though and I'm sure she can handle that part. I just applied the magnet test and that is negative, not even slightly drawn to a magnet. I'm gonna dig out my jewelers loup and look at the structure. I'll get back at ya with what I find.
I feel ya on the BS thing. Keep your machine turned on and tuned up.
Peace to you Dave,

Kelly

 

[woof!]

Radio Shack's got ohmmeters for less than $20. The digital cheapie is a lot better than the analog cheapie, I own and use both and know their limitations.

Most electrically conductive minerals are semiconductors, so you may have to poke around a bit to find a spot to get a good conductive reading if there is one to be had.

Magnetite is a high-resistivity semiconductor depending on the level and type of impurities it's got. However I doubt there's any magnetite on the planet that will read lower than 100,000 (100K) ohms. Most magnetite won't even give a reading on a 19.99 megohm max digital ohmmeter.

On the visual inspection of the crystals with a magnifying glass issue, you want to rule in or out galena (lead sulfide). Galena is cubic, and I've never seen galena in which the distinctly squarish crystal faces weren't in evidence. If you see squares in this stuff, it's almost certainly galena. If you don't, then by analogy with what I've found in the Franklins, it's probably cassiterite.

--Dave J.

 

[Eu_citzen]

I think Dave nailed it with the shell conglomerate.

However the other stone has me uncertain, I doubt it is related to ore formation of any kind.

Glue a magnet to a thin piece of line or rope.
Hold it in the higher end of the line/rope, then check for magnetism.
It will help to determine if it is weakly or strongly magnetic.

My first thought was some kind of rock (gneiss?) with cordierite or a different rock with prehnite. (diabase?)
Is the mineral more greyish-blue or? It looks more greyish on these pics, to me.

Do you have some kind of magnification at hand? (i.e. a loupe) Look for cleavage. (don't hear that to often, do you?!)

Here is one example of cleavage if your uncertain:
http://skywalker.cochise.edu/wellerr/mineral/orthoclase/6orthoclase-cleavage5.jpg

Notice the stair case like pattern? (Often quite 'shiny' when light is reflected from it)
That's an example of cleavage.

Mineralogy Database has a good library over mineral characteristics.
Just use the search function for, say, cleavage and get an explanation of it.
Google has several good pictures also.