I’m new to gemology and trying to learn more about three loose diamonds I came across. These were found in a storage unit that belonged to a deceased couple, so unfortunately, I don’t have any information about their origin.
The diamonds weigh approximately 5, 11, and 14 carats. They are opaque, with some having distinctive features and what looks like a very porous texture. I’ve taken photos of them, including some under a cheap digital microscope, to show as much detail as possible.
I’m hoping to get insights into what they might be. Could they be carbonados or just black diamonds? What kind of crystal structure might they have? I’d love to hear any thoughts on what to look for or how I might learn more about them.
As someone new to all of this, I really appreciate any advice or feedback. I’m here to learn and very thankful for any help you can give me!
Based on the images, the gemstones might be something other than diamond. It is really hard to identify just from images alone. There are a few tests you can do to help determine what they could be. The first test would be specific gravity.
Here is an IGS video link to a similar test setup. (I am not sure if this link is working correctly, though)
The formula for calculating the specific gravity of a gem is:
Diamond has an SG of 3.51 to 3.53. There are a few other stone species, that can have a similar SG, so this doesn’t completely rule out diamond if you measure somewhere in that range.
The Gemstone Encyclopedia here at IGS has an really neat advanced filter where you can narrow down the specific gravity range of potential stone species.
Let us know what you measure for SG and we can then start selecting other tests to perform.
Do you have a multimeter and if so, can you check to see if they are electrically conductive? To do this, you can set it to resistance (the ohm symbol) and touch the probes to the stone. If so, that is diagnostic, ie, not diamonds.
“Carbonado” and “black diamond” are the same thing. “Carbonado” simply refers to the chemical makeup of the black diamond, while “black diamond” is the general term.
While most diamonds are not conductive, black diamonds typically have inclusions (namely high relative amounts of graphite) that can make them conductive. A multi-meter test will not be diagnostic in this case. @PaulB36648
Bonus: Because of the presence of graphite and the poly-crystalline nature of black diamonds, they are (usually) tougher than their mono-crystalline counterparts.
Good to know, and thanks for the detail, it’s something I wasn’t aware of and it’s kind of cool info to boot!
I am guessing that strength and hardness are probably two different things (I am an admitted amateur), but aim curious if such black diamond (the stronger-than-diamond kind) are technically more than Mohs 10? Again, probably unrelated but it does seem that technically there are degrees of hardness that are not really contemplated in the Mohs scale, as useful as it is, and technically, there is a diamond hardness range around that 10 number, more and less to some small extent. Is that correct?
Thank you all for the responses—they’ve been very insightful!
For some background, I found these diamonds along with a stone in a box labeled “carbonado.” I’ve attached a few images to show their appearance and porosity. I also performed a scratch test using corundum on the faceted diamonds, they did not scratch any of the loose diamonds.
I’ve been in contact with a few people for further testing and will share updates as I learn more. Any thoughts on the images or recommendations for additional tests would be greatly appreciated!
Hardness is the resistance to being scratched. Toughness is the resistance to being chipped/cracked.
Diamonds, while the poster child for being the hardest, are notoriously brittle because of their crystal structure. Black diamonds get around this by being micro-crystalline, which is more resistant to being cracked. Anything with a cubic crystal structure is easy to split.
There is a saying: “Strike a diamond with a hammer, and it will shatter like glass, quartz splits in twain, jade rings like a bell.” Jade is the toughest of all gemstones due to its fibrous structure that effectively re-enforces itself. This is why jade has been used to make weapons.
There are a few things that are harder than diamond now. Lonsdaleite (Another carbon alletrope) is nearly 60% harder, forms in a hexagonal crystalline structure, and occurs naturally in meteorites. And has so far been too small to be useful in jewelry. There are also a few lab-specialty substances that are also technically harder.
Boron Carbide may have found its way into the black diamond simulant industry as well:
Boron Carbide has an SG of 2.52. The material is a ceramic with a porous microcrystalline structure. It bears some resemblance to several of the facet images you posted.
Although, you mentioned these were found in an abandoned storage unit. No idea how long they had been in storage, so this might be a long-shot.
Hi Troy and James and all,
Yes, I thought of the SG test as a first because it is so easy. It isn’t mentioned on the first video and I didn’t have access to the whole thing on the second, so let me state here that with those stones, you could use a very fine string, even perhaps a nylon one which wouldn’t absorb any water and a small gram scale which weighs to 0.01 ct (the cheap ones display to a hundredth but are probably only accurate to 0.02 ct. Since the stones are not likely to allow tying the string on, you can use CA (aka super) glue to glue the string onto the gem. The bond will last long enough to do the measurement and the glue can be scraped off easily with a fingernail or something that won’t scratch the stone. Then you just need to find a list of SGs in order to isolate the possible choices. Color and hardness estimate (it may be hard for a novice to get closer than plus or minus one or two Mohs units.) and dichroism ($20 dichroscope) may help eliminate other choices. The girdle of the one stone shown didn’t look like a typical “sugary” girdle of a diamond, but I’m not sure about that. I would also want to look at the inclusions, which looked like a lot of tiny, tiny bubbles, but might be something else, under a lot of magnification. The facet edges were worn and the polish wasn’t very good and the pavilion only had one row of facets, so I wondered what diamond cutter would take the trouble to cut a big diamond and do such a poor job. These are speculative “tells” but you have to think about them. I don’t have a list of prices for black diamonds, but three loose diamonds of several carats in size are not something you would usually find hanging around in an old box if they were worth much…I do see one website saying that treated black diamonds are going for about $300/ct. Natural untreated about $1000/ct. But there are also synthetics available, but I don’t know in what sizes or when these became available. Good luck with this puzzle, but remember, “if it seems too good to be true, it probably is.” -royjohn
