I've been thinking a lot (due to the design of a dungeon) about the properties of Adamantine. I find the sources at my disposal curiously uninformative about its value, so I have inferred some things and derived others, or simply made bold leaps of assumption. I want to share my ideas so that others may draw inspiration from them (or use them directly).
The weight of Adamantine is fairly simple to deduce. The Core Rulebook tells us the weight of certain Adamantine objects, for example the Adamantine Breastplate whose weight is the same as the conventional steel breastplate (as listed under medium armor). From this we can clearly infer that Adamantine has the same mass per volume as steel or iron.
This assumption may be erroneous. Adamantine is much harder than steel and so it may be that less of the metal is required to produce a comparable piece of armor and so it may actually be heavier per-volume. However, since the Adamantine provides damage reduction as its chief benefit I tend to discount this.
Having made this determination we can use it to determine the market value of the material.
The simple approach is to take an example item (the Adamantine Breastplate) and use its price and weight to get a gross price for Adamantine. Using this approach we get:
| Adamantine||340 gp|| 1 lb|
That's probably the best thing to do, as has been pointed out to me since I originally wrote this. My much more convoluted solution takes up the rest of this page.
I found this factor more difficult to determine. According to its listing under Special Materials Adamantine is found only in "rocks that fell from the heavens" (i.e. meteorites) and is so valuable that things made from it are "always of masterwork quality". Clearly its rarity is enormous, but not so great that it is unknown in the world. The closest equivalent to this that I could identify with a known value is Platinum (see its Goods and Services listing (Trade Goods- Metals, Platinum (pound)) in that Platinum is extremely rare and used to create masterwork items (although probably never weapons or armor).
Of course, Platinum deposits are not limited to meteorites, so it is entirely possible that Adamantine is actually far rarer than Platinum. Nonetheless I consider it a good enough analogue. My position may be somewhat swayed, however, by the fact that in my (home brewed) setting the origin of Adamantine is different.
So what of the gold piece value of Adamantine? The best guide that I could find for this was in the value added to items when produced in this material. In its description we are told that items of various categories have set price increases representing the rarity of Adamantine, but items in those categories have varying weights and, by inference, use different amounts of Adamantine. For this reason, when considering the value of Adamantine as trade goods, I decided to disregard that information or assume that it represents the price different when the material is readily available.
Instead I returned to its deduced rarity as an initial guide to the value of the metal. At first I assumed a weight-for-weight price parity, between Adamantine and Platinum, but it occurred to me that a pound of Adamantine ─ given that its density seems similar to iron ─ would be a far larger volume than a pound of Platinum. Thus I determined to link the value per volume. I still needed to work out a per-pound price for the metal in order to determine its market value, so I resorted to some real-world science (if you can call it science) and looked up the weight-per-volume of iron and platinum.
Using information from simetric.co.uk I found that the mass of Platinum is approximately 2.7 times that of iron, so I assign the same ratio between Platinum and Adamantine. This is rounded and does not give a precise result, but it's good enough for me. From this we can see that a pound of Adamantine must have a volume 2.7 times that of Platinum.
Since I decided to link the values of the two metals by volume, due to rarity, rather than by weight this also means that a pound of Adamantine must be 2.7 times the gold piece value of a pound of Platinum. This gives us a value of 2.7x500gp per pound of Adamantine, or 1,350gp per pound.
That price is for refined Adamantine; the metal in its pure form. But metals are rarely found pure, instead they are found in the form of ore. In order to determine a market value for Adamantine ore I returned, again, to its comparison to iron.
To be honest, I fudged the details a bit here. I considered looking up the proportion of iron in iron-rich asteroids or meteorites for the most appropriate comparison, but I failed to find the information and fell back on a well known iron ore: Haematite.
I have since been informed that iron meteorites
are commonly 80-95% iron with the remainder usually nickel. Therefore I think it is reasonable to assume that Adamantine meteorites may be considered 'pure Adamantine'. However, this does not change the fact that it is supposed to be supremely rare.
From what I've read (and I'm no metallurgist) good Haematite iron ore contains 60% iron by weight. Simple? Yes, too simple. It seems to me that, due to the effort involved in refining ore, its price can not directly match the value of the metal within. Instead, I decided to halve the value of the ore for the amount of metal that it would yield. So, for a given weight of Adamantine ore I assume a market value equalling 30% of that weight in finished Adamantine. Thus, a pound of Adamanine ore is valued at 405gp or, for simplicity's sake, 400gp. Adamantine ore is slightly cheaper, per weight, than pure Platinum.
These values could also be substituted for the official values of items crafted from Adamantine. So a 30 lb Adamantine Breastplate, instead of costing 10,200 gp, would cost 40,500 gp. An almost four-fold increase and one that makes it even more reasonable to subsume the cost of the item's masterwork quality, as suggested in the official material.
Alternatively, we could reduce my valuations and make a pound of pure Adamantine worth 340 gold pieces, a large fraction of the value of Platinum but a small fraction of my estimate.
For the purpose of using Adamantine, or its ore, as trade goods I apply the following values. (Where 10 lb of Adamantine Ore yields 6 lb of pure Adamantine.)
| Adamantine (pure)
||1,350 gp|| 1 lb
| Adamantine Ore (good)
|| 400 gp
|| 1 lb
If you'd prefer to retain the listed prices of Adamantine items, then a closer valuation (based upon the Adamantine Breastplate) would be:
| Adamantine (pure)
||340 gp|| 1 lb
| Adamantine Ore (good)
|| 100 gp
|| 1 lb