About synthetic corundum

Hey everyone… I have found this piece of purplish pink from local miners who were walking on alluvial deposit, first time I touched the stone it make me wonder how beautiful it was and clean, I have never met with this kind of stone, it was having little inclusions on it side so I decided to take it to the lab for more verification to see if it’s natural stone. The lab tested the stone and give me certificate to verify it’s genuine. But I met with couple ppl and said it might be synthetic bcoz it’s too clean inside. my question is, is it possible for synthetic sapphire to not showing any features or pattern to indicate it made from the lab ? Is cleaness can be the factor for gemstones to identify as synthetic especially those come from alluvial deposit?

if it was tested by a certified lab then your stone is natural.
if it was found in an alluvial deposit, how would a synthetic stone get there?
if it were synthetic, there would be characteristic indlusions depending on what process was used to grow it synthetically. (google inclusions in synthetic corundum gems)…
The surface of the stone is weathered and has a pitted frosted glass appearance…typical for an alluvial deposit. A synthetic would have to be tumbled polished rough to have that surface weathering but doing so would not cause small pits on the surface…

It looks like you found something good…

Caveats: it’s been known that large synthetics can be rought tumble polished to give the appearance of being alluvial… yours has a lot of surface pitting.

The certificate has to come from a reliable and honest lab… the GIA is the most expensive but is the standard bearer. Overseas labs at the local level have been known to collaborate with miners. Not all certificates are equal. you did not state what country the mine was in nor whether the lab was certified.

Thank you Mr Steven for your ideas, the issue is there has been with some bad attitude for big and clean gems such as corundum, so everybody think it’s not possible for the corundum to not have many inclusions.

The mine is Matombo, Morogoro in Tanzania near Mahenge mines, and the Lab is government lab in Arusha. I’m thinking of send that stone to my guy in USA to take it to GIA for certified then we can be able to get certificate and sell it for a good price. It’s among of the rarest gems

more caveats:

you are lucky to have inclusions in the stone… they can distinquish not only natural from synthetics but also what synthetic process was used to make it, if it were synthetic…Hydrothermal stones are the most expensive due to the time and pressure/temperature conditions used to grow it. Flux fusion stones are grown faster. Each process leaves characteristic inclusions and growth lines… Cheaper processes such as the Czochalorski pull melt, and Verneille also have characteristic growth lines and inclusions. Googling these processes and looking for the inclusions and growth lines is homework but worth doing… to look into the stone for clarity you will need an immersion fluid. The refractive index of water is 1.33 while that of corundum is about 1.77 with small variations along different axes. the difference between air and stone is too great to make optical analysis possible… water won’t do it either.

If you do have a natural corundum that is clear and or large size it would be worth something… other factors such as color, color saturation, play in… a light or even darker violet stone doesn’t make it as a ruby. Corundum gems come in all colors of the rainbow… rubies from central tanzanian (winza) alluvial deposits are higher in iron than their burmese counter parts… inclusions can take the form of iron minerals, and amphibolite instead of the usual rutile inclusions found in marble hosted rubies. The host rock is a metamorphic paleoprotozoic amphibolite… Nonetheless, color saturated clean red rubies are just as expensive on the market as Burmese.

Thank you Mr Steven, I have got big thing on your ideas. I remember the time I took it for the testing in the lab they allow me to go check it inside by using microscope and we found that inclusion it have it’s natural inclusions, no any other inclusions such as rutile, lines, bubble or anything, it was having little inclusion like feather on it side. The stone is too clean that why still make ppl to not believe even after testing. It’s scary stone. Those local miners didn’t have ideas what kind of stone until I met with them and check it’s surface texture and light up with UV light is when I found out it sapphire then I took it in the lab for more testing to make sure it’s genuine. I believe there’s another deposit which is not discover yet and have unique stones which has never seen on the ppl eyes. We wish we could get GIA lab branch in East Africa countries bcoz we are struggling to identify some stones from our experts !! They have right tools but sometimes they can’t give you accurate results from the testing instead they tell you to find another lab for more testing

If your lab already ID’d it as corundum by its optical properties, SpG, hardness and other easy to do field tests, you might have something good on your hands. If its clear, the size of it makes cutting it into a large gem worth the price. the color is off for a ruby, purple and pink sapphires are worth less than ruby but still it’s a natural stone. I think that you should send it to a real GIA lab for authentication and a GIA certificate. It should cut into a beautfiful large stone. The price range for purple sapphires can go from $50 to $500 per ct. You have something that’s bigger that 10 ct. How much does it weigh? you could have some $$$$ on your hands.

big clean stones come under suspicion because if they are indeed natural, they would be worth a lot.
alluvial stones tend to be of better quality than hard rock mined stones. the ones that survive washing down streams with other pebbles tend to be more durable because of a lack of cracks and other flaws that would break up a weaker stone as it gets pounded against other pebbles in a river bed. clear ones that come from good crystals survive the process. I would not expect to find rutile inclusions in your stone because of the geology of the source rocks… amphibolites are enriched in titanium as a whole. Titianium calcium amphibole has been used as a geothermometer for metamorphic rocks within the amphibolite facies. Calcic amphibolites are not as common as high iron amphibolites.
the feather inclusions in your stone are microscopic fractures.
If this stone is a natural stone with only a few feathers, it will be valuable.

Heat treatment with flux will fill in cracks with a glassy material. How much of it is corundum healing versus glass filling is still debateable. High temperature heat treatment is used. Treatment with heat should be detectable to a trained gemologist…

You have given me deep info of the stones, I really appreciate :raised_hands:t6:. Hopefully I’ll get good money from it after take it to GIA lab.

best of luck
please message me back when you have your stone examined by the GIA lab. I don’t believe that GIA will price it for you… they just certify it as natural and give you a statement of quality based on the 4 C’s.
If it is natural and of decent quality, you will have to find a buyer… the ultimate price is what a buyer is willing to pay for it and what you willing to sell it for. Getting it cut will enhance the value greatly, but there are expenses including cutting, lab fees, auction commissions, etc. Don’t expect too much out of it even if it’s very high quality because your expenses will add up and can’t be recouped. The first step is to get it definitively ID’s by the GIA lab. What to do next is up to you. If you decide to cut it, you will need to find an expert cutter… I have no experience in taking all of the steps from mine to wholesale. Good luck.

erratum: amphibolites are NOT enriched in titanium as a whole.