Quick answer: the most expensive gemstones ever sold at auction are colored diamonds, led by pink and blue stones. The 59.60-carat Pink Star sold for about $71.2 million in Hong Kong in 2017. There is no official “most worthless” gem, but the cheapest are common, abundant minerals like ordinary quartz, which you can buy by the pound. What separates the two ends is not just rarity. It is a mix of rarity, durability, beauty, and marketing.
The top of the market
Auction records tell the story of what buyers will actually pay:
- Pink diamonds. The Pink Star (59.60 carats) sold for about $71.2 million in 2017, still one of the highest prices ever paid for a gem at auction.
- Blue diamonds. The Oppenheimer Blue (14.62 carats) sold for about $57.5 million in Geneva in 2016. Blue diamonds get their color from trace boron, the same element that makes the famous Hope Diamond glow red after UV light.
- Jadeite. The Hutton-Mdivani necklace, 27 beads of top imperial-green Burmese jadeite, sold for about $27.4 million in 2014.
- Rubies and sapphires. Top unheated Burmese rubies have sold for over a million dollars per carat.
Notice that ordinary white diamonds are not at the top. Colorless diamond is common compared to strongly colored diamond. The price is in the color.
The bottom of the market
At the other end you have minerals that are beautiful but everywhere. Quartz is one of the most abundant minerals in Earth’s continental crust. Clear quartz points, milky quartz, and tumbled agate and jasper are sold by the pound. That does not make them uninteresting. A water-clear quartz point is a stunning natural object, and our post on clear quartz explains why it is one of the most scientifically important crystals on the planet. It just means there is enough of it for everyone.
Other contenders for “least valuable gem” include hematite, common pyrite, and low-grade garnet, which is crushed and sold as sandpaper and waterjet abrasive.
The four things that set a gem’s price
1. Rarity
Rarity is mostly a chemistry problem. Quartz is built from silicon and oxygen, the two most common elements in the crust. Minerals that need scarce elements or unusual conditions are rare. We dig into this in why some minerals are common and others are rare.
2. Durability
A gem has to survive being worn. That is partly hardness (see the Mohs scale) and partly toughness, its resistance to chipping. Some extremely rare minerals are worth less than you would expect because they are too soft or brittle to wear.
3. Beauty
Color, clarity, and brilliance matter enormously. A ruby and a cheap red garnet can look similar in a photo, but a fine ruby’s color is more saturated and it is harder. Within a single species, top color can be worth a hundred times more than mediocre color.
4. Demand and marketing
This one is human, not geological. Diamond prices owe a lot to marketing: the line “A Diamond Is Forever” was written in 1947 by an advertising agency working for De Beers, and it helped make diamond engagement rings a near-universal custom. Meanwhile, some gems that are rarer than diamond sell for less, simply because fewer people know about them.
Same element, opposite price tags
The strangest example of all: diamond and graphite are both pure carbon. One is the hardest natural material and among the most valuable; the other is pencil lead. The only difference is how the atoms are arranged. That story is in Diamond and Graphite: Same Element, Opposite Extremes.
What this means for collectors
If you collect minerals rather than jewelry, price follows different rules. Collectors pay for crystal form, locality, and condition. A well-formed crystal from a famous locality can be worth far more than a cut gem of the same mineral. That is why a Large Double-Terminated Herkimer Diamond Quartz — Fort Plain, New York from a known New York locality is a better collector piece than an anonymous tumbled stone, and why buying by the lot (see parcel or single piece?) is such an efficient way to start.
