Prospecting Felslate: Analysis

Prospecting felslate can be a very profitable endeavour. To figure out if it is profitable however we need to know the rates of rare and uncommon gems you get from prospecting. This post focuses on data analysis and if you just want to get into Legion jewelcrafting as a money making method make sure you check out my posts on the matter and my spreadsheet that will tell you everything you need to know.

I have been prospecting about 15000 felslate personally under the assumption of 15% rares per prospect. I wasnt actually sure about this number, and i havent been tracking my results, so I decided to dig through the posts with results on prospecting to find the true gem rates for prospecting. For Leystone it seems very straightforward as the numbers in the u/Glizzerd Spreadsheet seem to converge very nicely for leystone. For Felslate the uncommon gems have converged, but the rare rates have not. We also see that across all the gems where we can be reasonably certain of the results the red and green gems have half the drop chance of the other colours, so it is safe to assume that is is correct for rares from felslate as well.


The table below summarises the results in terms of numbers of rare gems.from the posts on woweconomy with atleast 5000 felslate prospected. I excluded the smaller samples as I believe they are heavily skewed towards the extremes, Either bragging about a very good batch or whining about a terrible one, and people generally tend to whine more than they brag when it comes to RNGesus.


Rare Gems Felslate Gems per prospect Source
352 10,560 16.67% Link
189 5,000 18.90% Link
258 7,295 17.68% link
208 6,000 17.33% link
1077 32,535 16.55% Link

Over the entire sample the average rate of rares per prospect is 16.99%. Which strongly suggests that the rate is above 15%.

Now I will go a bit into the mechanics of prospecting. When prospecting Felslate you can get between 2-5 rare gems per prospect (I can not recall getting 1 gem, but i haven’t tracked my prospects so please correct med if this is wrong). This means that whenever you are using prospect the chance of actually getting at least one rare gem is much smaller than the average rate of rare gems per prospect as the average number of rare gems when you do get them is larger than 1. I assume that Blizzard has chosen fairly round numbers and symmetrical distributions for their RNG as it just seems simpler.

If we go further into prospecting felslate one way of looking at it is that the game does two checks each time you prospect. First it draws to determine whether or not you get any rare gems at all. If you pass that then it determines what amount of the rare gem you get between 2-5. Now if we assume that the distribution is symmetrical, which would make sense as it’s easy then the average number of rares when you get at least 1 rare is 3.5. This holds regardless of how the distribution in terms of whether the extremes are more or less likely than the values in the middle as long as its symmetrical.

With a 3.5 average gems the chance of getting 2+ rare gems per prospect is the total rate divided by 3.5.

If we assume that the ratio of rares to uncommons is the same for Leystone and Felslate the rate of rares from prospecting felslate would be 16.66…%. This seems to be very much in line with the sample I am using here. If we divide it by 3.5 we find that the chance of a prospect yielding 2+ rares is 4.76%. The only knock against this assumption is that the numbers are not particularily “round” and usually the numbers used by Blizzard are simple and “round”. The other alternativ if this hypothsis holds true is 17.5% as the rate of rares per prospect. This would give 1.75% for red and green gems and 3.5 % for the others and divided by 3.5 you would get a 5% chance of getting 2+ rares per prospect. I assume that it would be easy to test these two hyopthesises statistically, but yous from lloking at the sample 16.67% is more likely as the observed rate is closer to 16.67% than 17.5% so I wont bother doing any more rigorous testing.

More importantly the fact that the average number of gems when you get rare gems is higher than 1 leads to felslate having way higher RNG than Leystone and you need to really prospect large amounts to make sure that your observed rate is close to the average rate. As the numbers in the first table shows you are converging on the true rate after about 5000 felslate in the samples i found on this sub.

The gem rates are presented below across the gem types:

Gem Felslate Rate Leystone Rate
Furystone 1.67% 0.5%
Pandemonite 1.67% 0.5%
Dawnlight 3.33% 1%
Shadowruby 3.33% 1%
Eye of Prophecy 3.33% 1%
Maelstrom Sapphire 3.33% 1%
Total 16.67% 5%


Gem Felslate Rate Leystone Rate
Sangrite 10% 3%
Chaotic Spinel 10% 3%
Azsunite 20% 6%
Queen’s Opal 20% 6%
Deep Amber 20% 6%
Skystone 20% 6%
Total 100% 30%


TL;DR: Average rate of rares per prospect for felslate is at least 16.67%. You need to prospect at least 5000 felslate to feel comfortable that you will be close to 16.67% rares per prospect. The rate of rares from Leystone is 5%.


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