Crystals Rocks Minerals Understanding the Difference

Are Crystals, Rocks or Minerals?

Here's a question that causes no end of confusion.  Are crystals, rocks and minerals or are rocks and minerals, crystals?

Understanding the difference can be confusing.  However, in recent years, it's been made worse as the word 'crystals' has started being widely used by those who use these materials for their metaphysical healing properties.

It's sometimes even used to describe synthetic materials like goldstone and opalite. 

So, let's look at what each one is and why they're different from each other.  

The crystals, rocks and minerals that we enjoy today are the result of a geological process that began with the formation of Earth some 4.5 billion years ago.

Samples from three geographic regions confirm their use for personal adornment can be traced back at least 100,000 years.  Tests have confirmed that beads created from mollusc shells are likely to have been strung to be worn.

Rocks used for art specifically in Africa have been dated back 30,000 years.
 
Throughout history, crystals, rocks and minerals have been a source of intrigue and fascination.  In addition to art and jewellery, they've been used as tools, carried as talismans and carved into luxury objects.  They have long been associated with status, wealth and power.

The belief they hold mystical powers and healing properties is well documented.  Stories and myths associated with various stones have been passed down from one generation to the next.

Today, rocks and minerals are widely used to promote health and well-being.  

Although crystal healing is a pseudoscience, it's hugely popular around the world.  In recent years, this alternative therapy has exploded and is now a multi-billion dollar industry.

The lure of crystals, rocks and minerals is universal and common to every human being on the planet.  Despite their widespread use, a great deal of confusion exists regarding what each one is.

These four words are often used interchangeably but each one represents a slightly different natural material. Using the word 'crystals' as a blanket term for all three has created even more confusion.

The word 'rock' describes a naturally occurring solid made up of more than one mineral.  Rocks tend to be quite hard, hence the idiom 'hard as a rock'.

The main types of rock are igneous, sedimentary and metamorphic.  All three form through a different geological process.

Minerals, which also form through a geological process, are naturally occurring solids with a specific chemical composition and crystalline structure.

Chemical composition refers to the identity and number of chemical elements in a compound. Water (the compound) is made up of two chemical elements, hydrogen and oxygen.

A substance with an internal crystalline structure is made up of crystals.  A crystal is formed from a highly ordered repeating arrangement of atoms.

The study of crystals is crystallography, rocks is petrology, minerals mineralogy and gemstones gemmology.

Geology is the study of the Earth, its history, the rocks of which it's constructed, their structure, where they came from, how they have changed over time and how they continue to change.

What are Gemstones?

When a crystal rock or mineral is cut and polished mainly (but not always) for personal adornment, it becomes known as a gemstone.

For a material to be officially classified as a gemstone it must have particular attributes.  The most important is colour although some gemstones are colourless.

Durability, beauty and rarity are the other primary characteristics that distinguish a gemstone from an ordinary stone.

Durability encompasses hardness, toughness and stability although the difference between hardness and toughness is often misunderstood.

Highly translucent gemstones tend to be faceted.  They're usually cut from individual crystals. Examples include ruby, topaz, smoky quartz and citrine.

Stones cut as cabochons tend to be aggregates which means the mineral's crystals have grown together as one large, shapeless mass. Examples include malachite, agate and turquoise.

Let's Talk About Crystals and Minerals

A crystal is a naturally occurring, inorganic solid made up of a highly ordered arrangement of atoms.  The atoms form a repeating three-dimensional pattern known as a crystal lattice.  'Inorganic' means 'not formed from living matter.'   

A typical crystal contains billions of atoms, actually, it contains quadrillions.

The shape they form when they come together is known as the crystal structure.  

Crystal structure refers to the ordered arrangement of atoms within a crystalline solid.  When atoms come together to form a crystal, they arrange themselves in a specific pattern.  The arrangement results in the external geometric shape of the crystal.

It's important to note that while the structure of the atoms can influence the overall shape of a crystal, external factors such as growth conditions and impurities can also impact its final appearance.

The formation and subsequent growth of crystals is called crystallisation.

The crystal structure of a specific mineral is always the same.  If it changes you'll end up with a different mineral.

Pyrite and marcasite have an identical chemical composition.  Both are iron sulphide minerals (a chemical compound of iron and sulphur).  The mineral that forms depends on how it crystallises, or in other words its crystal structure.

Another example is calcite, which has more crystal structures than any other mineral.  Although its chemical composition is identical to aragonite, they're different minerals.

A mineral's crystal structure is a tool for identification because it's unique and specific to each variety.

The crystal structure of a quartz crystal will always be the same.  Made up of one atom of silicon and two of oxygen, its chemical formula is SiO₂.  If it contains any other elements it wouldn't be quartz.

This diagram is an example of a repeating arrangement of atoms in a crystalline solid.

Where crystals are present in a naturally occurring solid the material is classed as a mineral.  Minerals are made up of crystals.

Some can be difficult to see because of their size or because they're tightly interlocked or fused together.  Others are large enough to be seen with the naked eye.

Crystals vary in size from a few millimetres to several metres.  The crystal's external shape is defined by its crystalline structure.  Cube-shaped crystals are one of the simplest and most common shapes.  They're often seen in pyrite and fluorite.

Matter is any naturally occurring substance with a mass that occupies space.  The three states of matter are solids, liquids and gases.  All three are made up of atoms but the specific arrangement differs for each.

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For a solid to be crystalline it must have a highly ordered repeating arrangement of atoms.  If the arrangement is disjointed or random, an amorphous or non-crystalline solid will form.  'Amorphous', which comes from Greek, means 'without definitive shape or form'.

Obsidian which is volcanic glass is an example of an amorphous or non-crystalline solid.  Another is man-made glass which is produced by heating sand.

The most common mineral in sand is quartz, which is a crystalline form of silicon dioxide.

Non-crystalline or amorphous solids are also known as mineraloids.

Crystals often grow when liquids cool and solidify.  If they cool too quickly there's not enough time for atoms to arrange themselves in an orderly repeating pattern.  The solid that subsequently forms will, therefore, not be crystalline.
 
Crystals can also form through the precipitation of water.  Water can only hold a certain amount of dissolved minerals and salts. As the quantity increases, they can no longer remain dissolved.  The particles then come together to form a solid.  An example of a mineral that forms in this way is halite.  Halite is rock salt.

While some crystals grow quickly, others can take thousands to millions of years.  The slower the cooling process the larger the crystals. 

Impurities within a crystal will often be partly or fully responsible for a change in colour.  Heat can also enhance or change the colour of a rock or mineral by altering its chemical composition.

Minerals are chemical compounds which means they're made up of two or more chemical elements.  The mineral quartz is composed of one atom of silicon, two of oxygen.  Water is made up of two atoms of hydrogen, one of oxygen.

A chemical element contains just one type of atom.  Minerals made up of a single element (one type of atom) are known as native elements.  Copper, carbon, gold, titanium and silver are all native elements.

What are Rocks?

Most rocks are made up of more than one mineral.  Approximately 5,000 minerals exist on Earth yet most rocks are formed from a combination of some of the most common.

Granite, which is a common igneous rock, is made up of the rock-forming minerals quartz, mica and feldspar.

Even though the minerals that makeup rocks are crystalline, the rock itself is not considered to be made up of crystals.  Rocks are aggregates or collections of minerals.  Their structure is often more complex than that of a single crystal.

In rocks, minerals are often intergrown or interlocked with one another.  This forms a solid mass without distinct crystal boundaries.

The arrangement and orientation of the minerals within the rock are influenced by pressure, temperature and the presence of other minerals, which is why they exhibit a range of textures and structures.

Some rocks, particularly those that are igneous and metamorphic, can contain visible crystals. Granite is one example. This is because slow cooling or intense pressure and heat allowed larger crystals to grow over long periods.

Even where larger crystals are present, the rock as a whole is not composed entirely of crystals.  It's a combination of minerals and other substances.

One way to explain a rock's nature and composition is to think of it as a solid mass made up of individual grains.  Imagine the grains have all been compacted tightly together.  Now, think of each one as a separate mineral.  The nature of each grain and how it fits together with the other grains defines a rock's hardness.

Rough grains that fit tightly together restrict the amount of room left for moisture, making this type of rock hard and non-porous.

Finer grains are likely to have a more rounded shape, so they won't lock together as tightly.  That leaves space for moisture and air so the rock will be softer and more likely to be porous.

All rocks begin life as igneous rocks but are altered over time by natural geological processes.  Igneous rocks form when magma (molten rock below the surface) or lava (molten rock above the surface) cools and solidifies.

Sedimentary rocks are made up of sediment that has come together underwater.  Layers gradually build up over time and, with the resulting pressure, become compacted together.  Through the process of cementation, the mass slowly transforms into rock.

An existing rock which undergoes a profound transformation caused by extreme heat or pressure is known as a metamorphic rock.

Minerals are only stable within a certain range of temperatures and pressures.  Once outside that range they break down and combine with other minerals within the existing rock to form a new mineral.  The process known as metamorphism mostly takes place deep within Earth's crust.