How Crystalline Solids & Amorphous Solids Differ

Instructor: Heather Pier

Heather has taught high school and college science courses, and has a master's degree in geography-climatology.

You may be familiar with what a solid is, but have you ever considered what gives a solid its shape? This lesson will provide you with an overview of the two main types of solids--crystalline and amorphous.

What Makes a Solid a Solid?

You probably would recognize a solid material if you saw it. We know that solids are a form of matter that has a definite shape, density, and volume.

Solids are firm, rigid materials that generally resist changes in their shape. Metals, gemstones, plastic, ice, and your bones are all examples of solids.

Other forms of matter include liquids, gases, and plasmas - all of which can easily be differentiated from solids simply by looking at them.

But did you know there are different types of solids? The two main categories of solids are amorphous solids and crystalline solids.

You can easily recognize whether something is a solid or not, but how can you tell what kind of solid it is?

Crystalline Solids

Crystalline solids are perhaps the easiest to visualize. Crystalline solids are solids that have a definite internal atomic structure that follows a regular, repeating pattern.

In almost all cases, the external appearance of a crystalline solid is a direct representation of their internal structure. For example, grains of halite (the mineral we commonly refer to as salt) are shaped like perfect cubes. Their internal crystal structure, made of atoms of sodium and chlorine, is also cubic like their outward appearance.

This regular internal chemical structure also causes crystalline solids to have well defined melting points. In terms of how these type of solids break, crystalline solids exhibit what geologists refer to as cleavage, which means they have the tendency to break along distinct planes in their crystal structure.

Almost all minerals (the most notable exceptions being obsidian and quartz) and many man-made materials exhibit crystalline structure.

Halite is a crystalline solid that has a cubic internal and external structure.

Amorphous Solids

Amorphous solids are nearly opposite in most ways from crystalline solids. They have irregular internal atomic structures, and as a result have a much more swirly and irregular-looking exterior form.

Glass is an amorphous solid, as is the volcanic mineral obsidian. Both have irregular, blob and swirl like surface appearances, particularly older glasses.

Amorphous solids also have irregular melting points, often transitioning from solid to liquid without a distinct point on the temperature where melting and liquefaction begins to occur.

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