4 Types of Crystals and Their Different Structures

When you think of crystals, glasses and jewelry might come to mind. However, crystals have all sorts of purposes from natural healing to electricity transformers. In the simplest form, crystals are geological rock formations. While some are still found through mining, many crystals are man-made because their structure is amazingly simple. With a bit of crystal knowledge under your belt, it’s time to look at the types of crystals found in the world.

Example of assorted crystals and gemstones Example of assorted crystals and gemstones

Types of Crystals

Crystals come in all different varieties including quartz, jasper, obsidian, citrine, turquoise, amethyst, and more. Most of the birthstones are a type of crystal. However, crystals can be broken down into four basic types based on the atoms that create them and the bonds they have. Learn about covalent, ionic, metallic, and molecular crystals.

Covalent Crystals

Covalent crystals are those crystals that are bonded together with covalent bonds. These bonds are extremely strong and brittle since the atoms share electrons to create the bond. Since these atoms are packed together and covalently bonded, these materials are extremely hard to break like diamond and quartz. Diamonds are even a 10 out of 10 on the Mohs Hardness Scale, and quartz is a 7.

Example of covalent crystal diamond

Ionic Crystals

Since covalent crystals use covalent bonds, it only makes sense that ionic crystals are created of ionic bonds. Ionic crystals are solid crystals with a high melting point, held together by the attraction of the ions (i.e. positive to negative). The most well-known ionic crystal is found in your salt shaker.

Example of ionic crystal table salt

Metallic Crystals

Metal isn’t the first thing to pop into your head when you think of crystals, but that is exactly what metallic crystals are composed of. Metallic crystals are made of metals and held together using metallic bonds. These crystals have a shiny appearance and include copper, gold, aluminum, and iron, to name a few. To see an example of metallic crystals, just look at a wedding band or car.

Example of Metallic Crystal copper plated penny

Molecular Crystals

The weakest of all the crystals are the molecular crystals. Held together by weak hydrogen bonds, molecular crystals have low boiling points and break apart relatively easily. Some you could even break apart with your hands. Dry ice is a great example of molecular crystals. You might even find molecular crystals in your pantry in the form of rock candy. Who knew crystals could be yummy?

Example of molecular crystal dry ice

Crystal Structures

The structure of a crystal is simple. While they can have all different unique shapes, at the atomic level, they are repeating patterns of atoms. How the atoms repeat is what creates the shapes of crystals. For example, crystals created from salt can form cube shapes, while carbons that form diamonds can make all different types of shapes of crystals. The seven different crystal structures include:

  • Cubic - common, simple cube shape
  • Hexagonal - flat top and bottom, and six sides like a hexagon
  • Monoclinic - a prism-shaped crystal
  • Orthorhombic - conjoined pyramid shapes
  • Tetragonal - rectangular shape like butter sticks
  • Triclinic - abstract forms
  • Trigonal - rectangular with triangle ends

The Different Types of Crystals

When it comes to classifying crystals, consider their bonds and their structures. Now you know there is chemistry behind diamonds, and not just fashion. Keep your chemistry knowledge going by looking at chemical properties.