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How are crystals made?

        Science | Minerals

Crystal Blue Persuasion
Perhaps the only type of crystal that you've tried catching on your tongue?

If all this talk of crystals has you itching to grow some yourself, you're in luck -- or not, depending on what you want to grow. Salt or sugar? Sure. Artificial diamonds? You'll soon see why even Bond villain Blofeld decided it was simpler just to smuggle them.

You can grow crystals in one of three major ways: from a vapor, from a solution or from melt. Let's look at each method one by one, beginning with vapor deposition.

The fact that crystals can grow from a vapor should come as no surprise. After all, atmospheric ice crystals -- we call them clouds and snowflakes -- do it all the time. They accumulate because the atmosphere becomes supersaturated with moisture: It contains more water than it can hold at a given temperature and pressure, so excess water leaves the gaseous state and aggregates into crystalline ice [sources: Encyclopaedia Britannica; Libbrecht].

Other crystal types -- silicon, for example -- can grow from gases supersaturated with key elements, but might need a little chemically reactive boost to do so [sources: Encyclopaedia Britannica; McKenna].

In most cases, the process begins with a tiny seed crystal to which other molecules attach, layer by layer, as they come out of suspension -- much in the way silver iodide crystals aid in "cloud seeding" by providing nucleation sites for ice crystals. The process requires great patience, but it produces surprisingly pure crystals [sources: Encyclopaedia Britannica; McKenna].

Growth from solution shares much in common with vapor growth, but liquid replaces gas as the supersaturated medium. Salt and sugar crystals created as science projects are good examples of solution-grown crystals. The solute approach outperforms gas deposition in terms of both growth speed and crystal size. Here's why: In a gaseous state, the vaporized substance whirls in a dizzy Viennese waltz among other gas molecules, and it can take a while for individual dancers to leave the floor and join the crystalline clique. A solution acts more like a high school slow dance, complete with crystalizing wallflowers that hang out near the surface, promoting faster growth. Its user-friendliness explains why the solution approach dominated synthetic crystal growth for many years [sources: Encyclopaedia Britannica; Zaitseva et al.].

The third method, growth from melt, requires first cooling a gas to a liquid state and then chilling the liquid until it attains crystalline solidity. The melt method excels at making polycrystals but can also grow single crystals using techniques such as crystal pulling, the Bridgman method and epitaxy. Let's take a closer look at each in the next section [source: Encyclopaedia Britannica].

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