Have a look at ajsgems.com, they have a few listed for sale. These are retail prices, private sellers tend to get a lot less.
Value is determined by a number of factors. Apart from the obvious size (bigger is more) cut and clarity, it’s the desirability and strength of the colour changes. Murky dull colours and slight colour changes are not valued as highly. Vivid colours and strong colour change are the most valuable.
Thanks for the responses, everyone. I'll have a go at posting the pics. To me the change is marked but then I certainly don't have enough experience yet. The stones are + 7 carats and clean
Are you looking to buy the rough or selling the rough?
Is someone cutting the rough material for you?
If you don't mind my asking, why buy rough material since there is an added element of risk compared to buying a cut stone. Final material is usually around 30% of rough at best. Colour can vary a bit depending on the cut selection, cut design of the finished piece and sometimes a clean stone can yield surprises in the final outcome. I've had a piece where the highly experienced lapidary came across an unexpected inclusion and the yield of the rough ended up as 10%.
Wow! thanks for the info and pics, Demantoidz. The second pic is exactly the colour shift I have. Really great to have all the details.
Chrono.
I'm not buying. The rough is part of a collection of stones we inherited. And I'm educating myself about them as I catalogue. (It's slowish process but I'm loving the journey.
I've just had a look at the Rough Stone Instagram site. Some of the less than clean stones I've sorted do have small black dots in them...
which suggests they come from Mahenge... Oh my word. So much to learn yet.:-/