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Treasure Companion 001-027.Pmd Part I Concepts & Premises 2.3 GEMS Gems have been valued for thousands of years for their beauty, rarity, and supposed magical abilities. Amethysts were thought to protect the wearer from intoxication and poison. Diamonds were seen as a remedy for all sicknesses. The beautiful green color of emeralds were not normally seen in other stones. For these reasons, and a multitude of others, individuals have fought and died to transport, sell, and mine these precious commodities. 2.3.1 PROPERTIES Gems are described by a variety of properties. These properties come from two areas. The first is the chemical composition of the gem. Most gemstones are minerals that have formed into crystals. The nature of these crystalline formations determines the transparency (how much light the gemstone will transmit), luster (the appearance of light TREASURE from a polished stone), specific gravity (a measure of COMPANION density), and hardness. There are many other properties determined by chemical composition, but these are the BH main ones that let jewelers tell one type of stone from the next. 13 The second factor that determines properties in gem- stones is the admixtures that occur within the stones. MOHS’ HARDNESS SCALE Admixtures are other minerals that occur in trace amounts Scale Reference Mineral Note and give color to many gems. If we look at a type of gemstone, such as corundum, we find that it is made of 1 Talc Scratched with Part I aluminum oxide. This chemical composition provides it 2 Gypsum fingernail Concepts & with its hardness, its transparency, its specific gravity, and Premises other factors. If the specific corundum has admixtures of 3 Calcite Scratched with a chromium, it will have a beautiful red color, though the 4 Fluorite copper coin. shade will vary depending on the amount of chromium, 5 Apatite Scratched with a and the jeweler will call it a ruby. If it has admixtures of 6 Orthoclase penknife bivalent iron with traces of titanium, then it is called a sapphire instead. 7 Quartz Will scratch glass 8 Topaz TRANSPARENCY 9 Corundum Transparency is the amount of light transmitted through 10 Diamond a substance. Transparency is effected not just by the chemical structure of the stone, but by its thickness color, SPECIFIC GRAVITY and the presence of flaws in the gemstone. A stone is considered to be transparent if light will pass through it as Specific gravity is its weight compared to the weight of if it were glass. Semitransparent stones will allow the outline an identical volume of water at a temperature of 4° Celsius. of an object to be seen through them. Translucent stones Specific gravity is related, but not quite the same, as the allow some light to pass through but one cannot see an density of an item and is an important means of telling one object, or its outline, through them. Non-transparent or gem type from another. Specific gravity is expressed in a opaque stones do not allow light to pass through them even ration of its weight per volume compared to the weight per in small sections. If a stone is both transparent and colorless volume of water. So a gem, such as an opal, with a specific it is often called lucid. gravity of 2.05 has a weight per volume that is 2.05 times greater than that of water. LUSTER Luster is the property of reflecting light from a gem’s 2.3.2 VALUE surface. The smoother the surface of a stone, the higher a The value of gemstones is based on a variety of factors. degree of luster the stone will show. This explains why It is hard to say what is the greatest factor for the value a stones that are harder (which can take a greater degree of gemstone. However, beauty may be a strong candidate. polishing) are often more luminous than stones that are not Gemstones, whether a transparent diamond or an opaque as hard. jet, add color and richness to the lives of those who own Stones with the highest degree of luster are called them. In societies (and times) where owning colors other adamantine (diamond-like). Some opaque gem stones such than brown or dun was seen as a sign of wealth, owning as pyrite and hematite have a metallic luster because they something as pretty as a sapphire certainly made the reflect light much like gold and silver do. Most gem stones individual stand out. have a vitreous (glass-like) luster. Vitreous luster covers a The second component to the value of a gemstone is large range of appearances and many gemstones (such as certainly rarity. Emeralds, for example, are very scarce and topaz) that are in this category are far more lustrous than this (combined with their beauty) leads to a great demand others (such as quartz). for these stones. Chrysolite, also called peridot or olivine, The weaker types of luster are resinous, greasy, and waxy. though it often resembles emeralds, is much more com- Certain fibrous minerals, such as cats eye, have a silky mon, and for that reason and others it is much less luster, while others display a pearly luster. If a gem has little expensive. or no luster it is considered to be dull. A third factor of value is quality. Many gemstones will come in a variety of grades which will range in luster, HARDNESS transparency, and color. Sometimes gems that are very The chemical structure of a gemstone gives it a specific common as mineral deposits will produce crystals large hardness or durability. This property is one of the most enough and with enough quality to be rated as gemstones, important ones for identifying the gem and is important even though in more common forms they have no particu- for determining its value (see below). At one time, the lar value. Certain combinations of the same stone (though border line between semi-precious and precious gems (see usually with different admixtures) will be more valuable below) was drawn by hardness alone. than others, such as the transparent red, lustrous fire opal, Hardness is rated on a scale from one to 10 with which is much more valuable than its rather dull white and diamond having the highest rating (at a 10) and talc having translucent cousin, hydrophane (or world’s eye opal). TREASURE the lowest rating (at a 1). Gems that are higher on the scale COMPANION will scratch those that are lower on the scale. On Earth this scale was invented by the German mineralogist Friedrich BH Mohs (1773-1839) and bears his name; the Mohs’ Hardness Scale. GMs should feel free to change the name 14 or simply refer to it as “the hardness scale” if they do not want to use Mohs’ name in their world. A fourth factor that is often of great importance is the GMs may wish to take the appearance of gems into hardness of a stone. Harder stones are generally more account in their world. Perhaps most of the gems are simple valuable than softer stones. Chrysolite, for example, is a tumbled or are Table Cut gems, but a few are cut by the beautiful green stone that is often mistaken for emerald. lapidaries of a particular race who make more beautiful Though it is a beautiful transparent stone that is very rare gemstones. Such stones might be worth many times their in some areas, it is not nearly as valuable as emeralds more common counterparts. GMs may wish to assign a Part I because it is very soft and is easily chipped and abraded. modifier such as x5 or x10 to the value of stones with more Concepts & Premises Consequently, chrysolite jewelry and gemstones do not modern facet cuts than those that lack them. retain their value as well as similar jewelry containing emeralds. This pushes the demand for the stones down, and 2.3.4 WEIGHT thus the price goes down as well. Gem prices are given in carats, which is a unit of weight. These four factors, and others (including society’s A carat is 0 .2 grams. This means that there are 5000 carats current fads and fashions), drive the price of gemstones. A to the kilogram, 2273 carats to the pound, and 142 carats GM should feel free to modify the prices given in the tables to the ounce. While it is certainly fine to keep track of gem in Part III if he thinks a particular stone would be rarer or weight, GMs may wish to allow their players to simply more valued in his particular world. ignore gem weight for encumbrance purposes. Players and GMs should also realize that gems are To provide a relative scale of size, the charts on the commodities to be bought and sold. They are not a form following pages include the number of carets in a 1 cm of cash. Most businesses are not set up to trade in gems, and diameter sphere of that gemstone. may not be willing to take them at other than a considerable loss to the characters (-50 to all Trading maneuvers unless you are dealing with a jeweler or a money changer). Jewelers (who pass the cost of gems on to their customers) 2.4 and money changers may well be willing to trade characters GEM GRADES cash for their gems (though they normally charge a fee of In various time periods different methods for rating the 1% to 5% of a gem’s value). value of gems have been used. One of the most common is a distinction between precious, semi-precious, and 2.3.3 CUTS ornamental stones.
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