What is a Diamond?

What makes diamonds so special? Different people have different answers to that question. A research scientist might say it’s the conditions under which diamonds form in the earth. An economist might say it’s their rarity. A consumer might say it’s their association with love and beauty. And they’d all be right.

The natural world is commonly divided into three kingdoms: animal, plant, and mineral. Members of the animal and plant kingdoms are alive—or were at some point. That means they’re organic. Minerals aren’t alive, and never have been: They’re inorganic. Diamond is a mineral. Other minerals are common table salt and the tiny quartz grains in beach sand.

Atoms are the basic structural units of all matter. Every mineral is defined by the types and relative quantities of its atoms. This is called chemical composition. It’s also defined by the arrangement of its atoms—its struc-ture—which is usually orderly and predictable.

Differences in chemical composition and structure give minerals their unique properties. Variations in either one can result in a very different min- eral. For example, the atoms in a spinel (a type of colored stone) are arranged in ways similar to diamond’s. But spinel is made up of different chemical elements.

A chemical element is a substance that consists of only one kind of atom. Most minerals are combinations of two or more elements. Colorless syn- thetic spinel, for example, looks a little like diamond at first glance. In fact, it was once used in jewelry as a common diamond imitation. But it’s made of three elements: magnesium, aluminum, and oxygen.

Diamond is the only gem made of a single element: carbon. Diamond is typically about 99.95 percent carbon. The other 0.05 percent can include one or more trace elements, which are atoms that aren’t part of a diamond’s essential chemistry. Some of them can influence its color or shape.

Formation conditions also help determine a mineral’s identity. Diamond forms under high temperature and pressure conditions that exist only within a specific depth range beneath the earth’s surface. Graphite, like diamond, contains only carbon, but its formation process is very different. The result is that graphite is so soft that you can write with it, while diamond is so hard that you can only scratch it with another diamond.

Without any one of these factors, diamond might be just another mineral. Fortunately, though, the magic combination of composition, structure, and formation gives diamonds the qualities that make them extraordinary.

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