Calculating the Value of Pretty Stones

I haven't touched on this for awhile, but it's relevant so I'll give some background.

Sorry I can't publish this in a larger format. It opens fine in another window, though.

The list here includes "ornamental stones," the commonest sort, the kind that Blaine recently referred to as "fish tank" rocks, which isn't far wrong. Yet while it's true that a "cherry-sized" rock that's an agate is worth a mere 30 c.p. in Budapest, I rush to point out that 30 copper coins weigh about 1.62 pounds, the same size agate weighs just less than 2/5ths of an ounce. Chat tells me it takes about 540 such rocks to fill the bottom of an 18 by 12 inch fish tank, which equals 16,376 copper pieces of value, or about 85 g.p., at a weight of about 13 pounds. 85 gold pieces weighs about 21 and a quarter ounces, so polished agates clearly aren't worth their weight in gold, but still, not bad.

I think the real issue isn't that "low price gems" don't have a meaningful value, it's rather that the encumbrance of things really isn't considered very closely, and most every "value" is compared to the player's need for the next experience level. 85 g.p. is not going to get a group of 5th level players very far down that road, so it feels pretty silly when that's all the gems are worth.

The table above is highlighted where the gemstone of that size is worth 5 g.p. or better on it's own. For the agate, that's a chunk the size of an apple, 8.65 cub.in., about the size of a Spartan. 540 of those would fill a chest that's two feet long, 18 inches high and 18 inches deep... or about five to six standard bushel baskets. Their total value would be 2,951 g.p. and their weight about 447 lb. That amount in gold pieces would weight 46 lb., for the sake of curiousity.

I promise, if I give that weight of agate to a party, they're going to figure out how to move 447 lb.

But, all this is old news. I've had these elements as part of my gems table for a long time. Why bring it up now?

Well, because the standard AD&D table produces a "10 g.p. gem," not a "10 g.p. agate," and I've never been able to reconcile the old table and my new work in a way that I could produce it quickly in game play. But, thanks to ChatGPT, I can now.

This is a basic, simple table, with every line representing a randomly generated gem. I've replaced the DMG labels of "ornamental, fancy, semi-precious..." et al because I've repurposed those labels for the gems themselves. The "bead" essentially equals the 10 g.p. category from the DMG, with the "bauble" equalling the 50 g.p. category and the "gemstone" being the 100 g.p. Here, the combination of "stone" with "gem" is meant to convey that we're not talking about shining glistening jewel that the hero reaches for in hand of the enormous statue in some treasure room... that would be a "brilliant." Gemstones are just the everyday decently valued "stones" that have beauty but a fairly ordinary presence in a lapidary's shop.

Simply explained, the "gem" (used as the general term) is rolled on the far left on a d100, adjusted from the DMG. I'm using 01-44 (bead), 45-69 (bauble), 70-85 (gemstone), 86-95 (gem), 96-99 (jewel) and 00 (brilliant). That's a sharp change from page 25 of the DMG, if you want to look it up.

The formulas get so long here that it's not practical to show them inside the table... so this part is just for the excel nerds. Normality shall ensue soon. But, here's an image for framing what's going on, showing just ten generated gems



The DMG stipulates that each stone gets a d10 rolled for it, and if a "1" is generated, then that stone goes up to the next category: that is, a bead becomes a bauble, a bauble a gemstone, a gemstone a gem and so on. I wasn't sure how to do this in excel, but ChatGPT managed it of course. This is the formula appearing in the M column:

=IF(L3=1,IF(B3="sm bead","bead",IF(B3="bead","bauble",IF(B3="bauble","gemstone",IF(B3="gemstone","gem",IF(B3="gem","jewel",IF(B3="jewel","brilliant","lg brilliant")))))),IF(L3=10,IF(B3="lg brilliant","brilliant",IF(B3="brilliant","jewel",IF(B3="jewel","gem",IF(B3="gem","gemstone",IF(B3="gemstone","bauble",IF(B3="bauble","bead","sm bead")))))),B3))

On a 10 rolled (no examples on the table), it downgrades the stone to the category lower. If a "brilliant" is pushed up, it becomes a "large brilliant;" if downgraded, a "bead" becomes a "small bead."

Thus, you can see that line 9 changed "bead" in column B to "bauble" in column M. That allows column N to reassess the value:

=IF(L3=1,IF(M3="sm bead",C3,IF(M3="bead",D3,IF(M3="bauble",E3,IF(M3="gemstone",F3,IF(M3="gem",G3,IF(M3="jewel",H3,IF(M3="brilliant",I3,J3))))))),IF(L3=2,K3*2,IF(L3=3,K3*(1+RANDBETWEEN(1,6)/10),IF(L3<9,K3,IF(L3=9,K3*(1-RANDBETWEEN(1,4)/10),IF(L3=10,IF(M3="sm bead",C3,IF(M3="bead",D3,IF(M3="bauble",E3,IF(M3="gemstone",F3,IF(M3="gem",G3,IF(M3="jewel",H3,IF(M3="brilliant",I3,J3))))))),K3))))))

This is doing a bit more. A roll of "2" doubles the original value, a roll of "3" adds 10-60% to the value; a roll of 9 reduces the value by 10-40%. All this is done automatically, so I don't have to think about it.

Column's O through R then do a second basic check, in which another 1 doubles the size of the gem. I did not use any other modifier for this column, because I really don't want to generate smaller gems. 5 g.p. is about as small as I want to bother about.

Then, the fun part. And oh, how I like this.

This shows the calculation for fitting in those gems that have been created by the pricing table correctly to the value generated by the table. Here, I'll show this without the formula, adding a few more lines and all the relevant columns:

There we are. Look at line 3: a roll of 78 produces a "gemstone" with a value of 100 g.p.; two worth checks adjust the price not at all, so that it remains what it was. BUT... and this is the absolute bliss of this thing for me:

Never again do I have to tell a player, "you find a 100 g.p. gem." Nope, it's a "tourmaline the size of an almond." The actual price of the thing is not a 100 g.p., as it happens, but that's how much x.p. I'm going to give for it. The price will matter as to where it is sold.

By the way, I don't know why there are five walnut-sized fire opals... I pressed refresh and got none. Just coincidence. Here's the lookup page for those interested, though it's not easy to read in this format.

For the first time in, what, nearly 20 years, I feel like I don't have enough varieties of gem. That's just awesome, I think.

This same structure more or less can be applied to jewelry, but I've just done a little bit of work with that so far. The look-up page can be effectively endless, but it is also has the unbelievable potential for work that will never end.

As such, when I pick up the next post on treasure, it'll be about magic.