How Much Do You Know About These Precious Gems and Metals?

Precious metals have a couple of things in common. One, they're rare. And two, they have economic value, either in jewelry or in some sort of industrial application.

Karat is a term that refers to the gold's purity. Pure gold is very soft, so it's typically mixed with other metals to make jewelry.

Most natural rubies undergo a process that improves their reddish color. This is a standard and approved practice in the gem industry.

It's the phrase jewelry marketers love to throw around -- 24-karat gold. That's the purest form of gold.

Diamonds are the hardest natural substance around. The only thing that can scratch them? Another diamond.

Copper is very useful, but it's not a precious metal. The precious metals are gold, silver, platinum, palladium, ruthenium, rhodium, osmium, iridium, scandium, hafnium and beryllium.

Opened in 1937, the United States Bullion Depository is brimming with much of the U.S. government's gold supply. There is approximately $180 billion worth of gold in the depository.

It takes an incredible amount of time -- at least one billion years -- to form a diamond. Some diamonds are three billion years old.

False, karat denotes the purity of gold. Carat, on the other hand, is a measure of a gemstone's weight.

Diamond sellers break the diamond trade into two categories: gem-grade, for jewelry, and industrial-grade, those used for a vast array of industrial purposes. Most mined diamonds aren't appropriate quality for jewelry, so they wind up as industrial products.

Platinum is incredibly rare. So rare, that it's one of the most precious of the precious metals. It's strength and lack of reactivity make it useful, and it's beautiful in jewelry, too.

Silver isn't just beautiful, it's useful, too. It's a very good conductor of electricity. It's also an excellent thermal conductor.

Pearls are the only gemstones in the world that are produced by a living organism. They are found in wild oysters ... but just 1 in 10,000 or so oysters produce a pearl.

Palladium is used in car catalytic converters. The metal helps to break down the pollutants in car exhaust so that they aren't so damaging to the environment.

The Cullinan Diamond was mined in the area of South Africa in 1905. At about 1.3 pounds, it's still the biggest uncut gem-quality diamond ever found.

The diamond was given to King Edward VII of the United Kingdom in honor of his birthday. It was cut into smaller diamonds that have been passed down to Queen Elizabeth II. Oh, to be a queen.

Rhodium is cherished in part for its high strength, which makes it suitable for a huge range of industrial purposes, from glass fiber creation to airplane spark plugs.

Pyrite is often called fool's gold. It looks a lot like gold, but if you tried to sell it on the market you'd look like, well, a fool.

Palladium has an amazing trait, in that it can absorb huge amounts of hydrogen. It's like a metal sponge, and it makes palladium useful in a lot of different industrial and automotive products.

Diamonds are nearly 100 percent carbon, and they form due to high temperatures and incredible pressure -- about 100 miles below the Earth's surface. They're then pushed towards the surface by volcanic activity.

Humans expend a lot of energy farming pearls in carefully-controlled conditions. Most of them are made in a freshwater setting -- but wild, saltwater pearls are much more valuable.

Gold is incredibly popular for personal adornment. The vast majority of the gold that's mined every year is used in jewelry.

Thanks to its great ability to conduct electricity, silver is widely used in the electronics industry. But don't go raiding your old VCRs for silver, because the metal is only used in small amounts.

Platinum is one of the least reactive metals known to humans. It almost never corrodes, one of the reasons it's so valuable for so many different purposes.

Amethyst is a type of quartz that's violet in color. It's popular in jewelry and it's also the birth stone for February.

Gold is very malleable and reflective. That reflectivity is great for jewelry, of course, but it also makes gold appropriate for windows and radiation shielding.

Sapphires are typically blue. But they also come in green, orange, purple or yellow, and they are sometimes even a blend of multiple colors.

As lovers of Old West lore surely know, panning is a means of separating gold from other minerals. In the days of the Gold Rush, a few hardworking (and lucky) people panned for gold and created a fortune for themselves.

Red diamonds are the holy grail of all diamonds. And at a price of roughly $400,000 per carat, they are ridiculously expensive.

Gemologist debate the source of a red diamond's coloring. But researchers suspect that it has to do with the way atoms are arranged when the diamond forms.