9.44 Crystals Definition & Facts

Crystals are not just diamonds, but unique formations of stacked atoms. Many crystals are made of minerals, but there are other types of materials that also make crystals. In this lesson, you will learn about what a crystal is, the types of shapes, and how they are formed.

What are Crystals?

What do snowflakes, table salt, and pencil lead all have in common? They are crystals. A crystal is a solid formation that follows a pattern as it shapes things such as salt, sugar, or emeralds. Although most people think of gems and diamonds as the only kind of crystals, they can be made of various materials. However, many crystals are made of minerals.

If you were to look at a single grain of salt under a microscope, you would see the unique shape of a cube. Salt is a mineral, and when found in nature it’s called halite. A mineral is a non-living natural substance from the earth.

Salt is a cubic crystal.
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When minerals become solid, they create a specific shape based on how their atoms are stacked. Atoms are the smallest parts of something. Imagine a cookie crumbling apart. All the crumbles are atoms, and when put back together, they form a cookie. Everything is made of teeny-tiny atoms that can only be seen with a microscope.

When a crystal forms, all the little specks of the mineral connect with each other like Legos. But unlike Legos, when minerals form crystals, they make a shape that has a pattern. In addition, every mineral makes a different shape because their atoms are different.

1. Main points:

Crystals are solid formations that follow a specific pattern, found in substances like salt, sugar, and emeralds. Many crystals are made of minerals, such as halite in salt, and their unique shapes are determined by the arrangement of their atoms. Each mineral forms a distinct crystal shape due to the differences in atomic structure.

2. Questions:

• Content Analysis: What is a crystal and what are some common examples?
• Thematic Analysis: How do the atomic structures of minerals determine the shape of crystals?
• Socio-cultural Analysis: Why might people commonly associate crystals only with gems and diamonds?

3. Further Discussion:

• How do you think the study of crystals can help us understand more about the natural world?

4. Answers:

• Content Analysis: "A crystal is a solid formation that follows a pattern as it shapes things such as salt, sugar, or emeralds."
• Thematic Analysis: "When minerals become solid, they create a specific shape based on how their atoms are stacked… Every mineral makes a different shape because their atoms are different."
• Socio-cultural Analysis: The common association of crystals with gems and diamonds likely stems from their visible and often striking appearance, which stands out more prominently than the microscopic crystal structures found in everyday substances like salt.

It’s All About The Shape

One of the most important aspects about classifying a crystal is by its shape. The shape has to be three-dimensional, and the atoms have to create a repeating pattern to form it. There are seven main groups of crystal shapes:

• Cubic crystals are shaped like a cube and can have up to 12 sides.
• Hexagonal crystals have six sides.
• Trigonal crystals have three sides.
• Monoclinic crystals look like a diamond-shaped box with many sides.
• Orthorhombic crystals are shaped like a rectangular prism (rectangular box).
• Tetragonal crystals are also like a rectangular prism, but one side is longer.
• Triclinic crystals look like slanted rectangular prisms because they don’t have 90° angles.

Amethyst is a hexagonal crystal formed from cooled lava.
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Crystallization

There are two main ways that crystals form, called crystallization. When molten lava erupts from a volcano, it eventually cools down. When it cools very slowly, then it can create crystals such as diamonds and rubies.

Another way that crystallization occurs is through water evaporating. Minerals are often mixed with water in nature, and when the water evaporates, the crystallized mineral, such as salt, is left behind.

1. Main points:

Crystals are classified by their three-dimensional shapes, with seven main groups based on their atomic patterns. Crystallization, the process of crystal formation, can occur through the slow cooling of molten lava, producing gems like diamonds and rubies, or through water evaporation, leaving behind crystallized minerals like salt.

2. Questions:

• Content Analysis: What are the different shapes of crystals and how are they classified?
• Thematic Analysis: How does the process of crystallization form different types of crystals?
• Socio-cultural Analysis: Why might certain crystal shapes be more recognizable or valued than others?

3. Further Discussion:

• How do you think the process of crystallization contributes to the diversity of minerals found on Earth?

4. Answers:

• Content Analysis: "There are seven main groups of crystal shapes: Cubic, Hexagonal, Trigonal, Monoclinic, Orthorhombic, Tetragonal, and Triclinic."
• Thematic Analysis: "When molten lava cools very slowly, it can create crystals such as diamonds and rubies… Another way that crystallization occurs is through water evaporating, leaving behind crystallized minerals like salt."
• Socio-cultural Analysis: Certain crystal shapes, particularly those that form well-known gems like diamonds and rubies, are more recognizable and valued due to their aesthetic appeal and rarity, which have cultural and economic significance.

Lesson Summary

Crystals are solid formations that are created by a repeated pattern of atoms. Atoms are the smallest parts of an element (like cookie crumbs) that cannot be seen. Many crystals are made of minerals, which are a non-living substance from the earth. Crystals form to make various three-dimensional shapes that can be found in nature.