So, I took these to a gemologist. What she old me was surprising.

[wondertuckian]

So, I took these to a gemologist. What she told me was surprising.

So, I dug this rock up a while ago, and it's been at the edge of my driveway for a while. Got to looking at it the other day and something just didn't look right. I had thought the small crystals in the rock were quartz, but upon closer inspection, there are some that seem to be octahedrons. So, I took it to a local jewelry shop and the gemologist put one under a microscope and said she thinks it might be opal. So, I asked her if she'd ever heard of opal in the area and she asked me where I got this from.
Me."My backyard."
Gemologist. "Well, it can't be opal, then."
Me."Well, what is it?."
Gemologist. "I don't know."

So.......what do you guys think?


Sorry Thread title should read: "So, I took these to a gemologist. What she told me was surprising."
not: "So, I took these to a gemologist. What she old me was surprising."

 

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[wondertuckian]

I think Spinel can be colourless. Hardness (if tested correctly) and crystal shape could fit.

You could be right. We had a couple polished chips of aqua laying around and it's difficult but will scratch it. So, it seems to be in that range as far as hardness. Some of the crystals look like there are trigons, but I've read, in the last couple days, that spinel can have them. What's got me confused is this: I've taken the stone to 2 gemologists and to a person studying to be a gemologist. One said the stones exhibited opalescence, one said they showed pleochroism, and the third saw neither. They all examined the very same crystal. The only explanation I can think of is that there's a fracture in the stone that, if light hits it at just the right angle, it would play tricks.
I'm really just trying to narrow down where this may have come from, and I have and idea that it may have come from fairly close. The picture of the rock in my original post (2nd to last) is the outside of the rock. As it's very rough and jagged, I don't think it traveled far. It was in an old stream bed, most of the other rocks are well tumbled, smooth/rounded.

 

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[wondertuckian]

Topaz is a good possibility

Your reply brought the story of the 16.25 carat Eagle Diamond to mind. I couldn't remember the name of the stone so it took me a while to find the story.
WISCONSINOLOGY: Murph the Surf and The Eagle Diamond

The Eagle Diamond (above) was the first documented diamond discovery in Wisconsin. In the summer of 1876, Charles Wood was digging a well through glacial drift in southwestern Waukesha County. “The digging had passed through 10 to 15 m of clay, and then through loose gravel, when a two meter layer of hard yellow material was struck. While penetrating this stratum, a hard stone of unknown identity was struck.” A few years later Wood’s wife, Clarissa, took the rock to a jeweler in Milwaukee named Samuel Boynton. Boynton initially identified it as topaz and paid Clarissa Wood $1.00 for the stone. Shortly thereafter, the stone was correctly re-identified by Boynton as a diamond. Clarissa offered to buy it back for $1.50. Boynton refused the offer and Mr. and Mrs. Wood sued him. The couple quite literally did not have any ground to stand on as they did not own (they rented) the land they were digging through at the time of the stone's discovery. The case eventually landed in the State Supreme Court in favor of Boynton. The stone, now valued at $700 was sold to Tiffany’s for $850. Tiffany’s sold it to almost richest man in the world J. P. Morgan, who eventually donated it to the Museum of Natural History.

 

[bwirth1999]

Considering the shape of the stone in the second pic, I would say fluorite is a possibility.. Not all of it, but that one at least.

 

[Eu_citzen]

You could be right. We had a couple polished chips of aqua laying around and it's difficult but will scratch it. So, it seems to be in that range as far as hardness. Some of the crystals look like there are trigons, but I've read, in the last couple days, that spinel can have them. What's got me confused is this: I've taken the stone to 2 gemologists and to a person studying to be a gemologist. One said the stones exhibited opalescence, one said they showed pleochroism, and the third saw neither. They all examined the very same crystal. The only explanation I can think of is that there's a fracture in the stone that, if light hits it at just the right angle, it would play tricks.
I'm really just trying to narrow down where this may have come from, and I have and idea that it may have come from fairly close. The picture of the rock in my original post (2nd to last) is the outside of the rock. As it's very rough and jagged, I don't think it traveled far. It was in an old stream bed, most of the other rocks are well tumbled, smooth/rounded.

I wonder if they found their license/diploma in a happy meal?

Opalescence can look similar to a fracture/cleavage inside the stone. It can fool a newbie.
Pleochroism is also impossible due to the cubic crystal structure of the specimens.

 

[wondertuckian]

Considering the shape of the stone in the second pic, I would say fluorite is a possibility.. Not all of it, but that one at least.

I ruled out fluorite as being way too soft. All the crystals I tried will scratch quartz. What I haven't ruled out is whether or not I'm dealing with more than one type of crystal. Even though they all look very similar, some seem to be hydrophobic, others, not so much. Whether that's due to some of the matrix remaining on the stones, I don't know. I am in the process of trying to polish off the remaining matrix in a rock tumbler, which should also narrow down further just how hard these are. We'll see if tumbling smooths or rounds them. Some have trigons, others not. Some are single crystals, but as I've gotten further into the stone I've found some that are in groups.

 

[Hitndahed]

Welp they are wrong...

Stone on far left in pic with the penny is a diamond :P

===========================================================
THAT IS MY EXACT THOUGHT.

Perfect octahedron shape. And look at that YELLOW host material.
Can someone please say KIMBERLITE?

Opal NO WAY,,, I have never seen any opal in this shape.
No wonder she asked WHERE you got it from.

I would really try to find out where that material from your driveway came from.

Hit

 

[wondertuckian]

===========================================================
THAT IS MY EXACT THOUGHT.

Perfect octahedron shape. And look at that YELLOW host material.
Can someone please say KIMBERLITE?

Opal NO WAY,,, I have never seen any opal in this shape.
No wonder she asked WHERE you got it from.

I would really try to find out where that material from your driveway came from.

Hit

There is a lamprophyre 30 miles (as the crow flies, about 40 miles drive) northeast of my house. That material came from an old stream bed that runs through my yard.
The lamprophyre is on one side of a terminal moraine, I'm, more or less, on the other. From the glacial maps I've found on-line, I'm just downstream of where 3 glacial lobes would have come together during the last ice-age.

 

[wondertuckian]

Here's a link to the report I found that briefly describes the six pack lamprophyre.
http://www.d.umn.edu/prc/lakesuperiorgeology/Volumes/ILSG_43_1997_pt1_Sudbury.CV.pdf
Pages 11 & 12.
An excerpt:

Various spinels are present in the heavy mineral concentrates. Some are reasonably Cr-rich, with up to
58 wl% Cr203 plus appreciable MgO and A12O3. Other spinels include magnetite and titanomagnetite.
Coarse honey-yellow to orange-brown zircon crystals are quite common. These grains are typically
rarely subhedral, and are mantled by fine-grained reaction products, possibly baddeleyite. A date 686 been obtained from these zircons using U/Pb techniques (Ashton Mining unpublished data). This
Importantly, the Six-Pak lamprophyre is diamondiferous; numerous small diamonds have been
recovered through caustic fusion techniques. Most diamonds are sharp-edged octahedra or macles, some
showing intricate surficial patterns including growth plates and trigons.
The discovery of the Six-Pak diatreme is very significant, as it is the first recorded mantle-sourced
diatreme to be identified in the southeastern Wisconsin region. The diatreme is also an enigma as it raises
numerous questions regarding the existence of other pipes in the area and their economic potential. Do the large
Wisconsin "drift" diamonds have a local source, or are they indeed derived from rocks far to the north in
Canada?

Funny thing is, is that it seems to be a pretty well kept secret, not one of the people I've talked to has even heard of it.

 

[PennyG]

Had to make a run down to Maywood, IL today, stopped in at the Lizzadro Museum of Lapidary Art in Elmhurst. Their gemologist spent some time looking at these crystals and came to the conclusion that they are probably zircon, but recommended taking them to a place in Chi-town just to rule out a slight chance they're diamonds. It was definitely worth taking a couple mile detour to stop in there, just wish I'd had more time to wander around & check it out.

When I lived in Highland Park I loved visiting the Lizzadro Museum . Lake Michigan produced so many beautiful rocks and fossils for me.

 

[Moesia]

Take a better picture of the crystals themselves.

 

[Moesia]

Also if you can have a closer look at the host rock for those crystals.