Crystals 101: The 7 Crystal Classifications


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Crystals 101

Class 3: The Seven Crystal Classifications

There are thousands of kinds of crystals, gemstones, and minerals on the planet, but on the molecular level, all crystals fall into one of seven categories: cubic, hexagonal, trigonal, tetragonal, orthorhombic, monoclinic, or triclinic.

What this means is in order for ANYTHING to be considered a crystal, its basic molecular structure must only be a square, hexagon, triangle, rectangle, rhombus, parallelogram, or trapezoid.

Wikipedia crrystal systems molecular structure diagrams

Diagrams of the 7 crystal systems from Wikipedia


So far, we know what crystals are physically, and from whence they come, geologically. If you missed the earlier lessons, catch up before reading on:
Crystals 101, Class 1: What Are Crystals?
Crystals 101, Class 2: How Do Crystals Form?

Now we’re talking about WHY crystals look the way they do. What’s the difference between, say, clear quartz crystal and apophyllite, which at first glance just appears to be another clear crystal?

Crystals are classified in one of the seven crystalline systems because of their molecular makeup. The basic molecular structures mean that the large form of the raw crystal will only ever display a shape based on its root/seed structure.

Iron pyrite (which you may know colloquially as “fool’s gold”) is a great example of a cubic structure. Large beautiful specimens of pyrite grow from the earth in a natural cube shape. If you were to drop or shatter the pyrite, the pieces would break into smaller cubic patterns.



Pyrite in its different forms. Some cubes are huge, some are tiny. Either way, it’s all cubic at the molecular structure. Click the photo to get your own piece of pyrite!

All the way down to the molecular structure, the tiniest unit of measuring the pyrite, you would see a cube. And no matter how large or small the pyrite is, it will never form a triangular shape.

Amorphous: The Crystal Classifications Exception

So there are 7 basic crystal structures, but there are always exceptions to every rule, and there is one final type of crystal structure called amorphous (from the Greek word “amorph,” meaning “without shape”). Minerals that fall into this category are classified as such because they do not possess a regular inner structure.

For example, moldavite is a mineral that is only found in one region of the world. It was formed when a meteorite crashed into earth. Moldavite’s creation was explosive and instantaneous!

On the other end of the time spectrum, another example of an amorphic substance is amber. Unlike moldavite, amber is fossilized tree resin that formed over a long period of time (mostly between 30-90 million years).

baltic amber crystals baby teething necklaces

authentic Baltic amber baby teething necklaces, direct from Lithuania! click the photo to get yours.


And because the tree resin consists of so many different substances (sometimes including insects and plants!), it does not have a geometrically regular molecular structure. Amber’s distinction is its age. Substances such as copal and frankincense resins are similar to amber, but cannot be classified as such because they are younger.



Examples of the different types of crystal classifications:

1. cubic: pyrite, fluorite, diamond, boji stones, sodalite, lapis lazuli, garnet

Fluorite crystal classification: cubic

Raw Fluorite

2. hexagonal: beryl, sugilite, morganite, emerald, aquamarine, apatite

Aquamarine tumbled crystals: hexagonal crystal classifications

Tumbled Aquamarine

3. trigonal: the quartzes (clear, rose, smoky, amethyst, citrine) agate, chalcedony, tourmaline, ruby, onyx, carnelian, jasper, heliotrope/bloodstone, hematite, calcite, aventurine

Clear quartz crystal & amethyst phalluses, rose quartz yoni eggs and spheres, and raw amethyst, rose quartz, and citrine crystals: trigonal crystal classifications

Carved clear quartz crystal & amethyst phalluses, carved rose quartz yoni eggs and spheres, and raw amethyst, rose quartz, and citrine crystals

4. tetragonal: apophyllite, zircon

apophyllite crystals: tetragonal crystal classifications

Raw Apophyllite crystal clusters. Notice they look like classic quartz, but are shaped slightly different.


5. orthorhombic: variscite, topaz, prehnite, peridot, aragonite

prehnite crystals growing atop epidote: orthorhombic and monoclinic crystal classifications

Prehnite (the light green) growing on top of some dark green epidote. As you can see, epidote has a very different molecular structure (monoclinic) from the orthorhombic prehnite, even though they grow in the same space.

6. monoclinic: chrysocolla, serpentine, nephrite, jade, moonstone, malachite, kunzite, epidote

moonstone: monoclinic crystal classifications

Moonstone Egg

7. triclinic: amazonite, kyanite, rhodonite, larimar, labradorite

labradorite crystals: triclinic crystal classifications

Polished labradorite

8. amorphous: moldavite, amber, opal, obsidian

obsidian crystal eggs: amorphic

Our Obsidian Eggs are amorphic because obsidian is volcanic lava which cooled to quickly to crystallize.


In the next class, we will discuss some practical ways to work with crystals.

Welcome to The Age of Eleven! Visit my website for a spectacular variety of crystals and gemstones, raw, polished and tumbled, loose and also fashioned into powerful handmade metaphysical jewelry with meaning.



About mizChartreuse

mizChartreuse is a writer, urban shaman and rebel creator of The Age of Eleven, an international lifestyle brand dedicated to recognizing the mystical in everyday life. She owns The Crystal Pyramid Room, a metaphysical center in Chicago.