Alternate Gem Info Gem Treasure Value Table (d100) D100 Base GP Value 01 05 02-03 10 04-06 25 07-13 50 14-25 100 26-35 250 36-45 500 46-71 1,000 72-85 2,500 86-95 5,000 96-97 10,000 98 25,000 99 50,000 00 100,000 This table is more appropriate for Companion or Master level treasures. For Expert level treasures, subtract at least 20 from the d100 results. For Basic level treasures, subtract at least 40 from the d100 results.
Once the value of the gems have been determined, the type of gem can then be determined / chosen. Gem Type Table (d100) 01 29 Affordable 30 54 Semi-Affordable 55 74 Unusual 75 89 Semi-Precious 90 95 Collectable 96 99 Precious 00 Special List of stones per gem type (partial list) Affordable: Amber, ametrine, andaluscite, chrome diopside, chrysoprase, citrine, common crystals / minerals, coral, iolite, kunzite, mother of pearl, obsidian, pyrite (marcasite), quartz & turquoise. Semi-Affordabe: Agate, amethyst, blue topaz, lapis lazuli, jasper, malachite, nephrite jade, onyx, peridot, rhodolite garnet, unusual crystals / minerals, white opal. Unusual: Beryls, bloodstone, common spinels, fire agate, moonstone, morganite, sunstone, zircons Semi-Precious: Aquamarine, fire beryl (goshenite), opals, pearls, unusual spinels, topaz, tourmaline Collectable: Alexandrites, black opal, black pearl, catseye (chrysoberyl), fire opal, garnets (normal & demantoid), Jadeite jade, tanzanite, unusual coloured topaz. Precious: Diamonds, emeralds, rubies/sapphires, star-collectable or semi-precious stones, tsavorite, tristals, unusual coloured alexandrites, unusual coloured tourmalines. Special: Star-precious stones, unusual coloured diamonds, unusual coloured tristals This list is incomplete to say the least. It does however present the most common gemstones found on earth. Now on other worlds, such as the Known/Hollow world, other gems may be found. As well, the valuations of certain gems may be different depending on how common they are. Diamonds would be worth a lot less if they were as common as coral. It is left up to the DM to create new stone types and ultimately decide what each type of stone is worth.
Once we have the value and type of gem, we can start to calculate just how heavy the gem actually is. The table below allows a rough calculation of how much, in carats, the given gem weights. Gem Type Value Per Weight Cut Stones Uncut Stones Affordable 1 gp / ct 1/5 gp / ct Semi-Affordable 5 gp / ct 1 gp / ct Unusual 10 gp / ct 2 gp / ct Semi-Precious 25 gp / ct 5 gp / ct Collectable 50 gp / ct 10 gp / ct Precious 100 gp / ct 20 gp / ct Special 500 gp / ct 100 gp / ct Weight of a carat (ct) While the RC gives one number, I haven't been able to figure out how it was arrived at. If a modern metric carat weight is used, 1cn equals 227ct. If the pre-metric carat weight is used this number varies from region to region resulting in a weight of 240ct to 180ct. Either way, the one gem = 1cn rule is a bit off, unless your game has some seriously big gems. For stones that are uncut, and thus less prone to value reducing damage it should be closer to 200ct (total weight in full or in part) = 1cn. Thus 190cts of uncut gems would equal 1cn, while 300cts would equal 2cn. Cut stones are a little different, since a scratch or nick by a harder stone could massively reduce the price of the stone. Even allowing for bits of cloth or paper wrapped around each stone to protect it 1 stone = 1cn seems a bit much. I would advocate 50ct to 100ct of protected stones = 1cn. Course grain cloth such as used hemp, discarded jute or scrap old clothing which would be all but free in most towns would be the 50ct benchmark. Fine silk or special paper, which would cost up to 1gp per ct weight of stone protected (but reusable), would be the 100ct benchmark. With most stones weighing well less than 5cts, a 10 to 20 (+) stones per cn seems more valid.
Variation Rules If the DM wants to change things up a little on the generic "ruby worth X gp (X cn)" and wants to vary the stone's worth via quality, size and clarity of the gems these tables can be used. Variable Gem Size, Quality (Clarity & Colour) & Cut Modification Table (d100) 01 25 Size 26 45 Quality 46 65 Cut 66 75 Size & Quality 76 85 Size & Cut 86 95 Quality & Cut 96 00 Size, Quality & Cut Gem Size Variation Results Table (d100) d100 Variation Gem Size (of base) Gem Value (of base) 01-09 Very Small 1/10 1/100x 10-24 Small 1/4 1/16x 25-50 Below Average 1/2 1/4x 51-75 Above Average 2 4x 76-95 Large 4 16x 96-98 Very Large 10 100x 99 Huge 20 400x 00 Gigantic 40 1,600x Gem Cut Variation Results Table (d100) d100 Variation (cut) Gem Value (of base) 01-09 Unacceptable 1/10x 10-24 Unskilled 1/4x 25-50 Common 1/2x 51-70 Uncommon 2x 71-85 Skilled 4x 86-97 Unusual 10x 98-99 Exquisite 25x 00 Unique 100x
Gem Quality Variation Results Table (d100) D100 (x2) Variation Colour Variation Clarity Gem Value 01 15 Cloudy Visible Flaws 1/5x 16 50 Inconsistent Slight Flaws 1/2x 51 85 Consistent Clear 2x 86 00 Flawless Flawless 5x
If the DM wants to provide a rough weight of the stone for the players, the following tables provides a quick lookup for that information. The GP value is determined, as well as they type of stone as normal. This information is then used to quickly find the rough weight (by ct) of the gem. GP Value / CT Weight By Gem Type Table (Base Cut Stones) GP / Type A SA U SP C P S 05 02 01 1/4 1/25 1/100 ---- ---- 10 03 01 1/2 01 1/6 1/25 1/100 ---- 25 05 02 01 1/2 01 1/4 1/16 ---- 50 07 03 02 01 1/2 01 1/4 1/100 100 10 04 03 02 01 1/2 01 1/25 250 16 07 05 03 02 01 1/2 1/4 500 22 10 07 04 03 02 01 1,000 32 14 10 06 04 03 01 1/2 2,500 50 22 16 10 07 05 02 5,000 71 32 22 14 10 07 03 10,000 100 45 32 20 14 10 04 25,000 158 71 50 32 22 16 07 50,000 224 100 71 45 32 22 10 100,000 316 141 100 63 45 32 14
GP Value / CT Weight By Gem Type Table (Uncut Stones) GP / Type A SA U SP C P S 05 05 02 01 1/2 01 1/4 1/16 ---- 10 07 03 02 01 1/2 01 1/4 1/100 25 11 05 04 02 01 1/2 01 1/16 50 16 07 05 03 02 01 1/2 1/4 100 22 10 07 04 03 02 01 250 35 16 11 07 05 04 01 1/2 500 50 22 16 10 07 05 02 1,000 71 32 22 14 10 07 03 2,500 112 50 35 22 16 11 05 5,000 158 71 50 32 22 16 07 10,000 224 100 71 45 32 22 10 25,000 354 158 112 71 50 35 16 50,000 500 224 158 100 71 50 22 100,000 707 316 224 141 100 71 32 Now you may notice that this is not a linear progression. The value of a gem is a function of many factors. Quality, cut and clarity is presented in the variation rules, but the size is the biggest determination of the ultimate price of the gem. The rough rule of thumb is that the value of the gem increases with the square of its weight. Thus a 4ct gem is worth 16 times that of a 1ct gem. The reverse is also true, a 1/5ct stone is worth but 4% of a 1ct stone. Now this is of course only a rough rule. Even in the real world this rule is not usually dead on, even factoring in other considerations. Ultimately the value of the stone is only what someone will pay for it, and not what the numbers say it should go for. DMs should keep this in mind that when the PCs/NPCs try to sell the gem and the buyers are only pay half what the numbers say the gem's worth.
More Exact Carat Weight Calculator For Cut Stones If the DM wants to generate an exact weight for cut stones the following formulas can be used. Keep in mind that uncut stones are at least 5 times larger than cut stones. Round faceted stones: Diameter squared x depth x SG x 0.0018 = ct Square cushion stones: Diameter squared x depth x SG x 0.0018 = ct Oval faceted stones: Length x width x depth x SG x 0.0020 = ct Emerald cut stones: Length x width x depth x SG x 0.0025 = ct Rectangular faceted stones: Length x width x depth x SG x 0.0026 = ct Square cut faceted stones: Length x width x depth x SG x 0.0023 = ct Marquise cut stones: Length x width x depth x SG x 0.0016 = ct Pear cut stones: Length x width x depth x SG x 0.0018 = ct Rectangular cushion cut stones: Diameter squared x depth x SG x 0.0022 = ct Square step cut stones: Diameter squared x depth x SG x 0.0023 = ct Rectangular step cut stones: Length x width x depth x SG x 0.0025 = ct
Cabochon cut stones: Length x width x depth x SG x 0.0027 = ct SG or specific gravity. This is how heavy the stone is per unit of volume relative to water. So a stone with a SG of 4.0 would be 4 times as heavy as an equal volume of water. A quick calculation for treasure is that a cubic foot of water is 62.5lbs (625cn) thus a one cubic foot pile of gems with a SG of 4.0 would weigh 250lbs (2,500cn). That giant treasure trove under that black dragon may just be a little heavier than most players think. Agate 2.55-2.64 Alexandrite 3.71-3.75 Amber 1.05-1.1 Amethyst 2.64 2.69 Ametrine 2.64 2.69 Ammolite 2.8 Andalusite 3.13-3.21 Apatite 3.1-3.3 Aquamarine 2.67-2.90 Aventurine 2.59-2.61 Beryl 2.6-2.9 Bixbite 2.66-2.7 Cassiterite 6.6-7 Chalcedony 2.56-2.64 Chrysoberyl 3.5-3.8 Chrysocolla 2.56-2.64 Chrysophase 2.58-2.64 Citrine 2.60-2.70 Cornelian 1.543 1.554 Corundum 3.90 4.10 Danburite 2.97-3.02 Diamond 3.50 3.53 Diaspore 2.58-2.64 Diopside 3.20-3.60 Emerald 2.67-2.90 Fire Beryl 2.55-2.64 Fluorite 3.20 Garnet 3.51 4.05 Green Amethyst (Prasiolite) 2.65 Heliodor 2.80 Herderite 2.90-3.00 Hiddenite 1.66 Idocrase 3.30-3.50 Iolite 2.53-2.66 Jade (Nephrite) 2.90-3.10 Yet Another Incomplete List - Specific Gravity Of Common Gems
Jasper 2.59-2.61 Kornerupine 3.28-3.35 Kunzite 3.15-3.21 Kyanite 3.56-3.68 Labradorite 2.70-2.72 Lapis Lazuli 3.71 Malachite 3.90-4.00 Moonstone 2.56-2.62 Morganite 2.71-2.90 Mother Of Pearl 2.60-2.80 Obsidian 2.33-2.60 Onyx 2.59-2.61 Opal 1.80-2.30 Pearl 2.60-2.78 Peridot 3.27 3.48 Pezzottaite 3.04-3.14 Pyrite (Marcasite) 4.90-5.20 Quartz 2.60-2.66 Rhodochrosite 3.40 3.70 Rhodolite 3.74 3.94 Rubellite 3.00 3.26 Ruby 3.90-4.10 Sapphire 3.90-4.10 Scapolite 2.56-2.77 Sillimanite 3.24 Sodalite 2.10-2.30 Sphene 3.40-3.56 Spinel 3.57 3.70 Sunstone 2.62-2.65 Tanzanite 3.10-3.45 Tektite 5.50-6.50 Tiger's Eye 2.65 Topaz 3.49-3.60 Tourmaline 3.00 3.26 Tsavortie 3.57 3.73 Turquoise 2.60-2.82 Zircon 3.90-4.73 Best of Dragon #2 (?) has a good list of substances and their weight in pounds per cubic foot under the How heavy is my giant articles. For SG just divide those numbers by 62.5. Others can be found on several places around the net. It should be noted that these numbers, for some reason, vary from site to site.
On-line Weight / Size Tables & Calculators: www.minerough.com/diamond-weight-size-formula.php (for common cut diamonds) www.gemoptions.com/sectionthree/pageone.htm (for common cut common gemstones) www.gemoptions.com/sectionone/pagefour.htm (for quick reference of popular faceted cuts) www.jjkent.com/articles (for light reading on gems and their history) www.dendritics.com/scales/carat-weight.asp (ct weight calculator) http://www.ehotbid.com/gemstone_info/infocenter/a-z_gemstones.html (basic reference for many types of gems)