You’ve probably heard the saying they’re not rocks, but did you know that crystals are solid natural forms? Crystal structures are not visible in many minerals, such as quartz, fluorite and opal. Crystals are composed of highly ordered atoms, and repeat in a three-dimensional pattern. For an object to be considered a crystal, billions of atoms must come together to form the pattern.
In order to be classified as a mineral, a material must be crystalline, meaning its atoms are highly ordered. Metamorphic minerals are created from a combination of heat and pressure. Marble, for example, was originally made from limestone. However, the different colours of marble are due to impurities that were introduced during metamorphism. The differences between a rock and a mineral are subtle, but it’s still worth looking at.
Some of the minerals you’ll find in nature aren’t rock at all, but minerals. In fact, they’re mostly a combination of other minerals. When molten rock cools, minerals form rocks. The solidified material then becomes crystals. The minerals begin to crystallize during the cooling process. The resulting rock is a solid chunk of rock. If you think of a rock as a solid mass of minerals, it will have a mineral structure.
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