A precious metal is a rare, naturally occurring metal that is less reactive than most elements, has a high lustre, is softer or more ductile, and generally has a higher melting point than other metals. These qualities attract us to the metal and thus we place a significant value to it. In general, the rarer something is, the more people will be willing to pay for it. Precious metals are rare and highly desirable. In Biblical times there were two precious metals, Gold and Silver. That has changed over time as we have been able to mine and refine more metals.
At one time aluminum was considered a precious metal since it was so difficult to extract from its ore. Napoleon III's most important guests were given aluminum cutlery, while those less worthy dined with mere silver. The pyramidal top to the Washington Monument, constructed in the late 1800s, is made of 100 ounces of pure aluminum. At the time of the monument's construction, aluminum was as expensive as silver. Today the period 5 and 6, group 8 through 11 metals are considered precious. These are most notably the group 10 and 11 elements - Gold and Silver, Platinum and Palladium with the group 8 and 9 to a lesser extent - Ruthenium and Osmium, Rhodium and Iridium.
Precious Metals are valued for their
Rarity, Inertness, Lustre, Ductility and Purity
Rarity, Inertness, Lustre, Ductility and Purity
So lets look more closely at what makes a precious metal. The list of characteristics goes like this:
- Rare - Either in quantity or difficult to refine
- Low Reactivity - Relatively Inert
- High Lustre - Can be highly polished
- Ductile - Easily shaped
- High Melting Point - Solid at reasonable temperatures
The first on the list is "Rare." An element can be rare because it is exists in limited quantities or because it is difficult to obtain as the free element. As an example Aluminum does not exist as the free element naturally so was considered a precious metal until such time as it could be extracted easily from its main ore, bauxite. It is not "rare" in abundance, being the third most common element and most common metal in the Earth's crust, making up 8% by weight. Gold, on the other hand, is found almost exclusively in the elemental form as nuggets or flakes but only makes up less than 0.000003% by weight of the earth's crust. Gold is truly one of the rarest of the naturally occurring metals. Platinum, Palladium and others are even less abundant.
Gold Nugget
Low Reactivity is next. This means the metal generally does not tarnish or form oxides on its surface. But it also relates to the formation of other minerals naturally, such as with Aluminum being most commonly found as bauxite. Noble metals are those metals that are resistant to corrosion and oxidation in moist air, unlike most base metals. Although a noble metal is not necessarily a precious metal, all of the metals listed above as considered precious today are noble metals. Platinum is the least reactive of all metals. Iridium is the most corrosion-resistant metal and is used to make crucibles and high temperature lab equipment. A unique property of Palladium is that one cubic centimeter can absorb 900cc of hydrogen. Platinum and Palladium are used extensively as catalysts.The third point is that the metal, when pure, has a high lustre or polished appearance. Lustre is a description of the way light interacts with the surface of the metal. Generally the metal will act as a mirror when polished. Glass mirrors are sometimes made with a thin layer of silver bonded to the glass with tin chloride. Lustre is generally appreciated when the precious metals are used for jewelry. Gold, Silver and Platinum, either alone or as alloys, are all highly valued for use in wedding rings, pendants or chains due to their color and reflectivity. Rhodium is often used to plate Gold and Silver to increase lustre and reduce tarnishing due to its very high optical reflectivity and low reactivity.
Next is ductility or malleability. These two characteristics speak to a metal's ability to deform under stress. Ductility relates to tensile stress or stretching and malleability refers to compression stress or being hammered or rolled into thin sheets. Many of the precious metals can easily be bent or shaped by hand if thin enough, unlike iron or steel which is difficult to bend, even in thin sheets. Gold is both ductile and malleable. One gram of it can be drawn into a wire almost 1 mile and a half long. It can be pressed into sheets only a few atoms thick. When pressed so thin it becomes transparent and is used on the visors of the astronaut's spacesuits to reflect infrared light. Gold is so soft that it generally can not be used in jewelry in its pure form (24 karat) but must be alloyed with other metals such as copper or silver (14 or 18 karat). Osmium is the densest natural element and is sometimes used in the tips of fountain pens to increase durability.
Lastly is the high melting point of the precious metals. Metals in general have high melting points. The precious metals all melt at temperatures above 1760o F, with Silver being the lowest (1763o F) followed by Gold (1948o F). In Biblical times silver would be refined by melting and then skimming off the dross, or contaminants, from the top of the molten metal. Gold would be refined in the fire by burning off any contaminants. Proverbs 25:4 - "Remove the dross from the silver, and out comes material for the silversmith. (NIV)"
| Name | Atomic Number | Relative Abundance | Melting Point (o F) | Color |
|---|---|---|---|---|
| Ruthenium | 44 | 1 ppb | 4233o F | Silvery White |
| Rhodium | 45 | 1 ppb | 3567o F | Silvery White |
| Palladium | 46 | 15 ppb | 2831o F | Silvery White |
| Silver | 47 | 75 ppb | 1763o F | Lustrous White |
| Osmium | 76 | 1.5 ppb | 5491o F | Silvery Blue |
| Iridium | 77 | 1 ppb | 4471o F | Silvery White |
| Platinum | 78 | 5 ppb | 3215o F | Grayish White |
| Gold | 79 | 4 ppb | 1948o F | Metallic Yellow |
Gold is considered the metal of kings. It has been treasured since antiquity. It was used for jewelry, in coins, decorative ornamentation and art. It signified wealth. The biblical record shows that it appeared to be relatively abundant (Solomon had tons of gold in his treasury!) and was used extensively in Solomon's temple at God's direction (1 Chronicles 28, ff). It represented wealth, purity and quality - "Worth it's weight in gold", "The Gold Standard" and "The Golden Rule." Its unique color, malleability and purity direct from the source (as nuggets or flakes) were prized characteristics. Even the streets of Heaven are lined with gold!
(Revelation 21:21b)
Zechariah 13:9 - "I will bring that group through the fire and make them pure. I will refine them like silver and purify them like gold. They will call on my name, and I will answer them. I will say, 'These are my people,' and they will say, 'The LORD is our God.'(NLT)"
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