We live in a world of crystals. You don’t have to dig deep into the Earth to find them. Even the bones in our bodies and the dust in the air contain crystals.
emerald crystals - Colombia

The largest emerald crystal on this calcite matrix measures 3.4 cm tall, 1.7 cm wide, and 1.4 cm to 1.8 cm thick. Cosquez Mine, Boyaca Dept., Colombia. © Rob Lavinsky, www.iRocks.com. Used with permission.

What are Crystals?

Gemologists define a crystal as a solid with its atoms arranged in “highly ordered” repeating patterns. Crystals can form in one of seven patterns known as crystal systems. Along with chemical composition, crystal systems define and distinguish mineral species.

For example, spinel has a chemical formula of MgAl2O4 – one atom of magnesium to two atoms of aluminum and four atoms of oxygen. It also has an isometric crystal system. That means its crystals have axes of equal sides that intersect at 90° angles. (This system is also known as the cubic system).

spinel

Minerals with isometric crystal systems can occur with octahedral shapes, like this cranberry-red spinel from Luc Yen, Yenbai Province, Vietnam. © Rob Lavinsky, www.iRocks.com. Used with permission.

The rocks that make up the planets in our solar system, including our own, consist of minerals. Composed of various elements, these minerals occur naturally in crystal form.

Esquel meteorite - a world of crystals

Sometimes, crystals can fall from the sky. This slice of the Esquel meteorite is billions of years old. It’s composed of an iron and nickel core with peridot crystals. Photo by Doug Bowman. Licensed under CC By 2.0.

Sometimes the rocks themselves have crystalline structures, too. However, rocks more commonly have polycrystalline structures. That means they’re made of aggregated materials that contain tiny crystallite grains.

lapis lazuli figurine

Lapis lazuli is a well-known gem material. Gem carvers often make beautiful objects from it, like this elephant figurine. Lapis is actually a rock composed of minerals from the sodalite group. Photo by Adrian Pingstone. Public domain.

What are Gemstones?

Many people probably visualize gemstones when they think of crystals. Indeed, gemstones make up some of the best-known examples of crystals.

What is a gemstone? The simplest definition is any mineral chosen for its durability and beauty and then cut and polished for adornment. Gem cutters or lapidaries can tumble, cab, facet, or carve gems.

faceted topaz - a world of crystals

Humans have cut and polished gemstones, like these large topaz pieces, for millennia. More recently, treatments have also been used to enhance their appearance, especially their color. For example, the iridescent blue gem is a mystic topaz. The rightmost orange gem is an Azotic topaz. Both are examples of coated gemstones. Photo by Michelle Jo. Licensed under CC By 3.0.

However, some popular gemstones aren’t crystals or even minerals. For example, amber forms from hardened tree sap from prehistoric trees. These pieces sometimes famously contain inclusions of insects and other creatures.

amber with mosquito

A mosquito trapped in Dominican amber. Photo by Didier Descouens. Licensed under CC By-SA 4.0.

Over many millions of years, gems form deep in the earth from minerals subjected to extreme temperature and pressure conditions as well as other forces. Of course, people have dug mines to reach gemstones, such as emeralds, rubies, and sapphires.

Tanzanian rubies - a world of crystals

Rubies from Tanzania. Photo by Jarno. Licensed under CC By 2.0

Gems sometimes reach the surface in other ways. When volcanoes erupt, they can bring up diamonds that form miles beneath the Earth’s surface. Surface erosion sometimes exposes gemstones, too.

turquoise vein

An exposed turquoise vein, discovered by Richard Edley while prospecting in the Mojave Desert. © Richard Edley. Used with permission.

The IGS gem listings contain information on hundreds of gemstones, from the very common to the extremely rare. Most (but not all) are crystals.

Crystals Closer to Home

Crystal particles also make up our mountains and form the ocean floor. However, you don’t have to search far and wide to find crystals. When you walk across sand, you’re walking on crystalline particles. Did you ever wonder where black sand comes from? Try to pick it up with a magnet. It will stick to the magnet because it contains the mineral magnetite, an iron ore.

black sand, Iceland - a world of crystals

Black sand beach, Selatangar, Reykjanes Peninsula, Iceland. Photo by Christian Bickel. Licensed under CC By-SA 2.0 DE.

Our homes, too, consist of crystalline and polycrystalline materials, like natural rock. Even artificial materials, like cement, get their strength from the growth of crystal particles.

Rocks, pebbles, and sand are all formed from eroded crystals. Like the rock they come from, these particles stay in the same crystal form even as they get smaller and smaller. Even airborne dust contains minuscule particles of quartz crystals.

dust on a glass turtle

Since dust contains particles of quartz, it can scratch the surfaces of many household materials and objects, like this glass turtle. Anything lower than a 7 on the Mohs scale of hardness is vulnerable. Photo by Avenue 51. Public domain.

Crystals in Living Things

The world of crystals even extends into living things. Kidney stones plague many creatures. Those found in dogs, cats, horses, and people may contain struvite, a naturally occurring crystal.

struvite crystals

Struvite under a microscope. Photo by RWTH Aachen, 2010/SuSanA Secretariat. Licensed under CC By 2.0.

Ever wonder why a pearl gleams in the sunlight? Sometimes, a tiny foreign object gets caught in a mollusk’s insides. The creature then secretes a fluid around the irritant. Like a scab on a skinned knee, this secretion protects against infection. This fluid, however, contains a crystalline mineral called aragonite. Over many years, the layers upon layers these tiny crystals form around the particle become what we know as a pearl. This layering of aragonite gives the pearl the sheen or orient that everyone loves.

pearl in oyster

A pearl in an oyster.

Crystals even form part of our bones and teeth. Hydroxylapatite, a variety of the crystalline mineral apatite, constitutes a principal part of our enamel and bones.

apatite

Apatite crystal from Slyudyanka, Russia. Photo by Kevin Walsh. Licensed under CC By 2.0.

Crystals abound all around us. From mountains to bones, from diamonds to dust, our world of crystals is vast and exciting.