These bouquets are created by growing crystals in solutions of different acid gradients.
As for size... this sample happens to have been grown on the Lincoln Memorial on the back of a penny.
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Noorduin found that as the crystals self-assembled, he could control their shape, size and direction of growth by altering the temperature, the amount of carbon dioxide allowed into the reaction and the acidity of the water.
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There are several interesting variations.
science.nbcnews.com