The base value of gems found in a treasure can be determined in whole or by lots of 5 or 10 stones by rolling d%:
 
 

Die Score	Base Value	Description	(or Size)	<Enc.(theory)>
01-25	10 g.p. each	Ornamental Stones	very small	1
26-50	50 g.p. each	Semi-precious Stones	small	1
51-70	100 g.p. each	Fancy Stones	average	2
71-90	500 g.p. each	Fancy Stones (Precious)	large	3
91-99	1,000 g.p. each	Gem Stones	very large	4
00	5,000 g.p. each	Gem Stones (Jewels)	huge	5

Value of a gem depends upon its type, quality and weight.
A huge semiprecious stone - carnelian, for example - is worth as much as an average gem stone, quality being equal.
Size may vary from stone to stone, a 50 g.p. ornamental stone being of above average size,
while a 50 g.p. gem stone would most likely be very small.

Ulaa (goddess of gems)

Q: How do you determine the value of
gems found during an Oriental adventure?

A: Use the gem section of the 1st Edition
Dungeon Masters Guide (pages 25-26) or
the 2nd Edition DMG (page 134) to determine
values and properties of gems.
(151.8)

<
Encumbrance Value of Gems
very small & small = 0.1#
average = 0.2# (2 is an easier number to work with than 3)
large = 0.3#
very large = 0.4#
huge = 0.5 #
>

<
As a quick rule of thumb, all gems start out at average size: increase this or decrease this by one size category for each increase or decrease in base value.
>

<go with the Enc.(theory) above: this is a good example of where game school takes precedence over realism/simulation.>
<it ain't like that in real life - thanks to bloatedblowfish for pointing this out!>
 

Increase Or Decrease Of Worth Beyond Base Value:
If you do not place specific value on each gem in a treasure, showing rather the base value of each gem instead, then variation in the worth of each stone should be allowed.
This variation will generally result in some increase, although there is a chance for decreasing value as well (see below).
To find if a gem increases in value, roll a d10 for each stone, and consult the table below:
 

Die	Result
1	Stone increases to next higher base value; roll again ignoring results above 8.  Stones above 5,000 gold piece value progress as follows:  10,000 GP, 25,000 GP, 50,000 GP, 100,000 GP, 250,000 GP, 500,000 GP, and 1,000,000 GP -- the absolute maximum.  No stone may increase beyond 7 places from its initial base value.
2	Stone is double base value. Do not roll again.
3	Stone is 10% to 60% above base value. Roll d6 to find new value. Do not roll again on this table.
4-8	Base value shown is unchanged.
9	Stone is 10% to 40% below base value. Roll d4 to find new value. Do not roll again on this table.
0	Stone decreases to next lower base value; roll again on this table, ignoring any result below 2.  Stones below 10 gold piece value are: 5 GP, 1 GP, 10 SP, 5 SP, and 1 SP.  No stone may decrease beyond 5 places from its initial base value.

When base value only is known, use the table above, and roll for each stone.
Stones for which a 1 or a 0 is rolled must be diced for again on the table, but all others are excluded from such rolls.
If large numbers of stones are in question, it is suggested that they be diced for in groups in order to make the process less time-consuming.

KEY TO GEM PROPERTIES
transparent (no notation)
translucent (italics)
opaque (*)

<>
ORNAMENTAL STONES, Base Value 10 g.p.:
 
 

d12	Name	Reputed Magical Property	Weight
1.	Azurite*: mottled deep blue	-	-
2.	Banded Agate: striped brown and blue and white and reddish	Restful and safe sleep	-
3.	Blue Quartz: pale blue	-	-
4.	Eye Agate: circles of gray, white, brown, blue and/or green	Restful and safe sleep	-
5.	Hematite*: gray-black	Aids fighters, heals wounds	-
6.	Lapis Lazuli*: light and dark blue with yellow flecks	Raises morale, courage	-
7.	Malachite*: striated light and dark green	Protection from falling, Wards off spells, evil spirits, and poisons	-
8.	Moss Agate: pink or yellow-white with grayish or greenish "moss markings"	Restful and safe sleep	-
9.	Obsidian*: black	-	-
10.	Rhodochrosite*: light pink	-	-
11.	Tiger Eye: rich brown with golden center under-hue	-	-
12.	Turquoise*: light blue-green	Aids horses in all ways (but stone shatters when it operates)	-

SEMI-PRECIOUS STONES, Base Value 50 g.p.:
 

d13  (d20, reroll)	Name	Reputed Magical Property	Weight
1.	Bloodstone*: dark gray with red flecks ()	Weather control	-
2.	Carnelian*: orange to reddish brown (also called Sard)	Protection from evil (Benefits wisdom)	-
3.	Chalcedony*: white <image>	Wards off undead	-
4.	Chrysoprase: apple green to emerald green	Invisibility	-
5.	Citrine: pale yellow brown	-	-
6.	Jasper*: blue, black to brown ()	Protection from venom	-
7.	Moonstone: white with pale blue glow ()	Causes lycanthropy	-
8.	Onyx': bands of black and white or pure black or white ()	Causes discord amongst enemies	-
9.	Rock Crystal: clear	-	-
10.	Sardonyx*: bands of sard (red) and onyx (white) or sard*	Benefits wisdom + Causes discord amongst enemies	-
11.	Smoky Quartz: gray, yellow, or blue (Cairngorm), all light	-	-
12.	Star Rose Quartz: translucent rosy stone with white "star" center	-	-
13.	Zircon: clear pale blue-green ()	-	-

FANCY STONES, Base Value 100 to 500 g.p.:
 

d14  (d20, reroll)	Name	Reputed Magical Property	Weight
1.	Amber: watery gold to rich gold (100)	Wards off diseases	-
2.	Alexandrite: dark green (100)	Good omens	-
3.	Amethyst: deep purple (100)	Prevents drunkenness or drugging	-
4.	Aquamarine: pale blue green (500) ()	Wards off foes	-
5.	Chrysoberyl: yellow green to green (100) ()	Protection from possession	-
6.	Coral*: crimson (100)	Calms weather, safety in river crossing, cures madness,  stanches bleeding	-
7.	Garnet: red, brown-green, or violet (the most prized) (100) (500) ()	-	-
8.	Jade: light green, deep green, green and white, white (100)	Skill at music and musical instruments	-
9.	Jet*: deep black (100)	-	-
10.	Pearl*: lustrous white, yellowish, pinkish, etc. to pure black (the most prized) (100) () (500)	-	-
11.	Peridot: rich olive green (Chrysolite) (500) <>	Wards off enchantments (Wards off spells)	-
12.	Spinel: red, red-brown, deep green, or very deep blue (the most prized) (100) (500)	-	-
13.	Topaz: golden yellow (500)	Wards off evil spells	-
14.	Tourmaline: green pale, blue pale, brown pale, or reddish pale (100)	-	-

<peridot, chrysolite: is that 2 different gems? if so, make 2 different entries>

<
Quick Generation (500 gp gems)
1. Aquamarine
2. Garnet (violet)
3. Pearl (pure black)
4. Peridot (Chrysolite) <?>
5. Spinel (very deep blue)
6. Topaz
 
 

GEM STONES, 1,000 or more g.p. Base Value
 

d14  (d20, reroll)	Name	Reputed Magical Property	Weight
1.	Black Opal: dark green with black mottling and golden flecks ()	-	-
2.	Black Sapphire: lustrous black with glowing highlights (5,000)	Aids understanding of problems, kills spiders, boosts magical abilities	-
3.	Diamond: clear blue-white with lesser stones clear white or pale tints (5,000) ()	Invulnerability vs. undead	-
4.	Emerald: deep bright green ()	Wards off foes	-
5.	Fire Opal: fiery red	-	-
6.	Jacinth: fiery orange (Corundum) (5,000)	Luck travelling, wards off plague, protection from fire	-
7.	Opal: pale blue with green and golden mottling	-	-
8.	Oriental Amethyst: rich purple (Corundum)	Prevents drunkenness or drugging	-
9.	Oriental Emerald: clear bright green (Corundum) (5,000)	-	-
10.	Oriental Topaz: fiery yellow (Corundum)	Wards off evil spells	-
11.	Ruby: clear red to deep crimson (Corundum) (5,000)	Gives good luck	-
12.	Sapphire: clear to medium blue (Corundum) ()	Aids understanding of problems, kills spiders, boosts magical abilities	-
13.	Star Ruby: translucent ruby with white "star" center	Gives good luck	-
14.	Star Sapphire: translucent sapphire with white "star" center ()	Protection from magic,  Aids understanding of problems, kills spiders, boosts magical abilities	-

<
Note that corundum gems are extremely hard.
They should get a save bonus (+2? +4?) vs. crushing blow & normal blow -- see DMG.80.III & DMG.81.DMS.
>

<
Quick Generation (1000 gp gems)
1. Black Opal
2. Emerald
3. Fire Opal
4. Opal
5. Oriental Amethyst
6. Oriental Topaz
7. Sapphire
8. Star Ruby
9. Star Sapphire
0. Roll again
>

<
Quick Generation (5000 gp gems)
1. Black Sapphire
2. Diamond
3. Jacinth
4. Oriental Emerald
5. Ruby
6. Roll again
>

<with regards to quick generation, an extended table could be done, that has individual entries for each of the color variants.
the color of a gem is important when one wants to TALK with azer>

Jewelry:<cf. OSRIC.310>

The base value of jewelry is determined by percentile dice roll, just as with gems:
 

Dice Roll	Base Value	Description
01-10	100-1,000 g.p.	Ivory or wrought silver
11-20	200-1,200 g.p.	Wrought silver and gold
21-40	300-1,800 g.p.	Wrought gold
41-50	5,00-3,000 g.p.	Jade, coral or wrought platinum
51-70	1,000-6,000 g.p.	Silver with gems
71-90	2,000-8,000 g.p.	Gold with gems
91-00	2,000-12,000 g.p.	Platinum with gems

Once jewelry's base value is determined, each piece should be checked
for workmanship and design by rolling a 10-sided die. Each 1 rolled
indicates the piece of jewelry in question is of exceptianal value and thus
either goes to the highest possible value in its class or to the next higher
class (where its base value is re-determined and its workmanship and design
are again checked). Any piece of jewelry set with gems must also be
checked for the possibility of an exceptional stone in the setting.
Any score of 1 on an 8-sided die indicates that the value of the piece of jewelry increases by 5,000 gold pieces,
    and these exceptional pieces are further checked by rolling a 6-sided die, each successive 1 doubling the increase,
    ie., 10,000 g.p., 20,000 g.p., 40,000 g.p., 80,000 g.p., to a maximum of 640,000 gold pieces.
The Dungeon Master <DM> can, of course, name what each piece of jewelry is
(bracelet, brooch, crown, earrings, necklace, pendant, ring, tiara, etc.),
giving its substance and the number and value of its stones.
 

Q: In the AD&D game, do gems and
jewelry have to be sold before a
character can get experience for
them? The DMG seems to indicate
that they must be converted into
gold pieces first. The DMG also
refers to conversion into a trans-
portable medium before experience
is awarded. What constitutes a
transportable medium? Do magical
items have to be retained and used
before experience is awarded for
them?

A: Gems and jewels don?t have to be sold,
but the experience value of these items is
equal to their sale value in gold pieces.
The DMG says treasure must be removed
from the dungeon and converted into a
transportable medium (i.e., carried on the
character?s person) or stored in a character
?s stronghold (residence). That is, treasure
must be taken to a safe place,
appraised, and assigned to PCs before any
experience is awarded for it. A transportable
medium can be anything the PC finds
convenient. Likewise, experience is award.
ed for items that are added to a character
?s hoard, use notwithstanding. No
experience is awarded for an item sold for
cash or traded for goods or services.
(142.10)
 

REPUTED MAGICAL PROPERTIES OF GEMS <when done, this whole section can be edited>
<beryl isn't listed in the tables: both emerald and aquamarine are forms of beryl: the magical properties for beryl have been placed there>
<carbuncle isn't listed ... no problem ... move all the notes (2 row table) to the FF ...>
<Cats' eye agate isn't listed ... should be included ... see FRA for the placement>
<Jet isn't listed ... should be included ... see FRA for the placement>
<Sunstone agate isn't listed ... should be included ... see FRA for the placement>
    <note: it is listed as Malachite & Sunstone : i have assumed that these apply to both ... the 2nd line of magical properties has been added to malachite>
<Olivine isn't listed ... should be included ... see FRA for the placement>
<Serpentine isn't listed ... should be included ... see FRA for the placement>

<Creation/Fabrication/Enchantment/Whatever: each of the magic items should have this field ... gems should be incl., as appro ...>
    <for scrolls, there is a "Scroll Creation" field that is at the bottom of the spell description : Ed Greenwood's Pages from the Mages are a good example>
        <there is a note about Alternate Material Components (*PH.64) ... if it's listed as a scroll ingredient ... it should be able to be used as (potent) AMC*>
                <maybe, have the scroll ingredients in a table format, with a column for AMC effects ... try to keep as simple as possible>
                    <actually, might just be clutter, try this:>
                        <MC: normal material component>
                        <MC+: an alternate MC that provides a greater effect. in some cases, this will be a link to a greater version of the spell>
                        <MC-: might be there in some cases ...>
                        <note: only one MC can apply. if more than 1 is readied, the hierarchy would go from + to normal to ->
                <example: READY(AMC) + CAST = a potentially powerful spell ... >
                <i would say that the gems would, overall, give the greatest benefit as an AMC ... perhaps the ink bases should be ignored ...>
                <an idea: if a gem is used**, one possibility is that a 'Greater' version (the "next level/version up") of the spell is cast>
                <for example, i READY my chrysoprase, then i CAST invisibility>
                    <suprise!! ... it says CHARACTERX casts INVISIBILITY, 10' RADIUS>
                <if you go with the 'Greater' for the AMC effects, then it is recommended, to keep things simple, to just go with the "next level/version up">
               <i'm thinking in UA(spell research) terms, as well ... code reusability ...
                all of these "next level/version up" spells are not too hard to do, once the main spell has been made ...
                when a character decides to engage in spell research, all of the "next level/version up" spells are going to be there,
                along with the other possibilities (to put a sane limit on it, i would say, limit the spell research lists to the WSC/PSC) ...
                yes, that's a big spell list that you can access when you decide to research ...>

* "Substitute materials might be allowed", PH.64 ... read BtB, this only applies to MU spells, as far as i know ...
** "such substitution could affect spell range, duration, area of effect, effect, etc." (PH.64)
        (possibly : etc. includes 'Greater' versions of the MU spell, but (as a rule of thumb) only in the case of gems"

Gem Type or Color	Effects or Uses
Agate	Restful and safe sleep
Alexandrite	Good omens
Amber	Wards off diseases
Amethyst	Prevents drunkenness or drugging
Beryl	Wards off foes
Bloodstone	Weather control
Carbuncle	Powers of dragon's sight
Carnelian	Protection from evil
Cats' eye agate	Protection from spirits
Chalcedony	Wards off undead
Chrysoberyl	Protection from possession
Chrysolite	Wards off spells
Chrysoprase	Invisibility
Coral	Calms weather, safety in river crossing, cures madness, stanches bleeding
Diamond	Invulnerability vs. undead
Hematite	Aids fighters, heals wounds
Jacinth	Luck travelling, wards off plague, protection from fire
Jade	Skill at music and musical instruments
Jasper	Protection from venom
Jet	Soul object material
Lapis Lazuli	Raises morale, courage
Malachite	Protection from falling
Malachite & Sunstone	Wards off spells, evil spirits, and poisons
Moonstone	Causes lycanthropy
Olivine	Protection from spells
Onyx	Causes discord amongst enemies
Peridot	Wards off enchantments
Ruby	Gives good luck
Sapphire	Aids understanding of problems, kills spiders, boosts magical abilities
Sapphire, Star	Protection from magic
Sard	Benefits wisdom
Serpentine	Adds to wile and cunning
Topaz	Wards off evil spells
Turquoise	Aids horses in all ways (but stone shatters when it operates)
Black	The Earth - darkness - negation
Blue	The Heavens - truth - spirituality
Clear	The Sun - luck
Green	Venus - reproduction - sight - resurrection
Red	Hemorrhaging control - heat
White	The Moon - enigmatic
Yellow	Secrecy - homeopathy - jaundice

<note: if there was more than 1 version of a gem, i applied the reputed magical property to all versions>
    <star sapphire is a sort of 'exception' : it was given the properties of both 'sapphire' and 'star sapphire' ... it is a special gem ...>

<sardonyx was another special case: it was given the reputed magical properties of both sard & onyx>

<note: i am using symbolic colors ('the exceptions' : based on the classic Netscape 4.7) here>
    <this is explained in the <note> at Appendix K ...>

<just a touch of color: wand of negation>
<just a touch of color: Spellcasting in Darkness (DSG), ea.>
<just a touch of color: ressurection, rod of ressurection = green**>
    <in theory, the symbolic colors are base/defaults: any shade of green could(should) be used ... >
<just a touch of color: jaundice curative, at artichoke>

NOTE REGARDING THE MAGICAL PROPERTIES OF GEMS, HERBS, et al.

Regardless of what qualities gems, herbs,
and other substances are purported to possess,
the mere possession of a score of a type of gem or a bale of some herb will convey absolutely no benefit of magical nature to
the character concerned.
These special qualities are given herein merely as information for Dungeon Master use in devising special formulae for potions, inks, etc.
The information might also prove useful in other ways, particularly with regard to description of magic items, laboratories, and so on. Under no circumstances should you allow some player to convince you to the contrary!
 

Dang, Treebor!

That's impressive to me, especially because I love gemstones, mainly the colored ones...perhaps set off by diamonds or pearls... 
I'd love a chest full of diamonds, corundum and other colored gemstones to admire even if those stones were a penny a carat!