On Searching Coin Shops For Hidden Gems

Takes me back to my Geology classes.

From what I've seen, most dealers check for diamonds and return those to the customer.
As for the rest, perhaps they're sold or simply tossed out. Jbuck--LOL, I guess I like being an "educator"--as long as I know something!

Sometime today I'll post how to tell quartzes from the nicer stones.

Eaglefoot--
I grew up in the shadow of a volcano and found lots of cool agate as a kid. Particularly nice too--some was bright orange/red.
Those large amethysts are pretty amazing. The small cut stones are pretty but not particularly valuable. I'll follow up soon on how to tell quartz from the better gemstones.

My younger brother used to have a small shop, kind of a new age store. He also traveled around on the show circuit. Probably 75% of his merchandise was various types of crystals, minerals & fossils. I bought an amethyst geode half from him at the grand opening of his store. It came from Brazil & stands about 14" high by 8" wide. Unfortunately I can't post a picture because the wife is visiting relatives & took the camera with her.

I have seen similar pieces priced anywhere between $350-1500, depending on how hoity-toity the store was. My brother used to buy these by the pound from someone who was importing them & would buy 300 to 500 lbs at a time. I picked mine out of a group of about 20, mainly because it was the deepest purple.

Nice find! It sounds like obsidian, and there are quite a few sources that were traded among the native populations. From what I've read, Obsidian is chiefly silica, iron, and magnesium. I found an obsidian point locally that's around 250 miles from the nearest source:



Jim,
Yes, those tsavorites are very nice...I suspect I have two here. I do know how many synthetics are very good--almost indistinguishable, and I've read on some great diagnostics, particularly transmission spectra, but that isn't exactly an "amateur" method, LOL. Yes, gemologyonline has some good info, thanks! If I can locate more stones like I have, I may just get into the more complicated diagnostics--I like complex details.

My next post will simply help a person sort by hardness into basic groups, where only special equipment/expertise can take it further.

Eaglefoot—yeah, obsidian is high-silica lava that cooled too quickly for crystals to form. We have a few volcanoes around here, but no obsidian—it's a special case in eruptions.

Regarding your dad's amethyst—I would think an older piece would be genuine too. I suppose every stone is simulated today, although I have less concern here because my small amethysts have no real value. That said, an amateur like me can distinguish some real from sim stones by looking for tell-tale inclusions specific to that mineral. In the case of amethyst, real stones often have some color zoning which is apparent by rotating under a light source. Outside of obvious inclusions, more valuable stones such as rubies are fairly complicated to tell between real and synthetic. It usually requires lab equipment that I don't have.

Now, taking the sorting process further: if you've sorted your stones against the hardness of window glass (5-5.5), the next step might be to compare your stone against a quartz sample such as agate. Since it's possible at this point to damage a real gem like garnet against quartz, so I'd recommend taking some precautions. Using a polished agate, pick a robust or hidden area on the question stone such as the girdle (meeting point of the crown and bottom facets) to lightly draw across this surface. Stop once you feel resistance. This means either your stone cuts the agate, or the agate is harder than your stone. Taking a loupe, inspect the area on the agate. Any evidence of a scratch suggests the stone is at least as hard as quartz, meaning 6.5-7.

Now here's where some subtlety comes into play: if your stone easily cut into the quartz, and left a thin, deep crack.it may be significantly harder than quartz. On the other hand, if the stone left a dull scuff, it may be quartz or something close in hardness. At this point, I would start comparing visible properties such as color, inclusions, and refractive indices of known stones against samples in question. These three factors should help point you in the right direction, although sorting synthetics is much harder.

I could continue with my analysis if there's interest—just let me know; I too am learning as I go along.

Yes--that happens whenever I find something cool and do more research to satisfy my curiosity. I think knowledge is the key to success, where knowing just a few details has helped me find some great coins!

The same could be said about mineralogy and gemstones, although the details are several orders smaller, more complex and difficult to discern. This is a real science with all the rigor and complexity that entails.

My exercise here simply attempts to sort gems by hardness. At best, it only determines what a stone cannot be, rather than work as a definitive ID. For example, a deep red gem that doesn't easily scratch agate cannot be a ruby because of the dramatic hardness difference between corundum (9) and quartz (7). It stands a better chance to be a garnet if corroborated by other physical properties.

At this point, if you have a sapphire watch crystal to sacrifice, you could test the harder stones. I should note there's a slight risk to softer stones, which is why I use a highly polished surface of a crystal. Using a hidden area of the stone, very lightly draw against the surface without any force. Here I've found that corundum will easily scratch a watch crystal, while topaz, beryl, or emerald at a hardness of 8 will not. Using a loupe lets you be very light and risk little damage to softer stones.

For stones that pass the sapphire crystal hardness test, you're left with the possibility of corundum, real or synthetic--or yet another stone of similar hardness. Most corundum can be sorted with a UV light because it will fluoresce a dramatic red/pink with a fuzzy boundary on the stone. Further discernment between natural and synthetic stones can be very complex, with a few exceptions. Many natural corundum stones such as sapphire and ruby contain inclusions easily visible under a 10X loupe. The most visible is the mineral Boehmite, and its presence is a strong clue of a natural ruby or sapphire. Better stones are tougher to tell from their synthetic counterparts, requiring microscopes and other lab equipment for positive ID.


It's probably obvious by now just how complex this gets, so I'll just end with a few links for further research

Gemstone hardness tables

A good resource for physical properties of minerals

More info specific to corundum:
Inclusions found in natural rubies

More on corundum inclusions