What is a Mineral? Geology 101: Minerals Part 1

Ask a room full of intro geology students whether a snowflake is a mineral and almost every hand says no. Ask why, and someone will tell you it's because no two snowflakes are alike. Chris Bolhuis has been asking that question for 25 years — he asked it of a young Jesse Reimink sitting in his high school classroom — and the answer is the whole point of this lesson.

It's been a while since we've released an episode on the Planet Geo feed, and there's more coming (plus a few projects we can't wait to announce). In the meantime, we're sharing the intro chapter of our Camp Geo audio textbook — the first lesson of the Physical Geology course you'd take in your first semester as a geology major. Several podcast platforms now display chapter artwork, which is close to how the Camp Geo mobile app works, so this is also a bit of an experiment: tell us how it lands.

Chris and Jesse start where geology starts: the five criteria something has to meet to be a mineral. It has to be solid, naturally occurring, inorganic, have a definite chemical composition, and have a definite crystalline structure. The first three are easy (though "inorganic" is on shaky ground as mineralogists warm to biominerals — this rule may not survive the decade). The last two are where students get hung up, so they slow down: quartz is always SiO2, halite is always NaCl, and swap potassium in for sodium and you've got a different mineral entirely.

Then a quick tour of the chemistry you half-remember from high school. Chris blows an atom up to the size of a 30-seat classroom — the nucleus is the tip of a pencil dangling from the ceiling, and everything else in the room is electron cloud. Jesse walks through protons, neutrons, and electrons, and why the loosely held electrons are what drive bonding. Ionic bonds transfer electrons (sodium hands one to chlorine, and a cation and anion snap together); covalent bonds share them. Chris's "paw-sitive" mnemonic and Jesse's parenting advice about covalent bonding are both, by mutual agreement, terrible. They both work.

The episode closes with the analogy that ties it all together: a five-gallon bucket of tennis balls dumped on the floor. There's one best way to stack them. Add a bucket of marbles and the best way to stack changes — a different composition forces a different structure. Because there is a definite chemical composition, there is a definite crystalline structure. Elements make minerals, minerals make rocks, rocks make the planet.

And then Jesse quizzes Chris. Chris goes one for two and files a formal complaint about question number two.

In this episode

• Why we're releasing Camp Geo content on the Planet Geo feed (and what's coming)
• The five criteria for a mineral — solid, naturally occurring, inorganic, definite chemical composition, definite crystalline structure
• Why "inorganic" may get dropped from the definition as biominerals gain acceptance
• Quartz vs. halite vs. the potassium version — what "definite composition" really means
• Is a snowflake a mineral? Working through all five criteria (yes, and you're a snowflake too)
• The classroom-sized atom and the pencil-tip nucleus
• Protons, neutrons, electrons — and why electrons do all the bonding work
• Ionic bonding: sodium, chlorine, cations, anions, and "paw-sitive"
• Covalent bonding: sharing electrons instead of stealing them
• The tennis-ball-and-marble analogy for crystal structure
• Definite composition → definite structure → minerals → rocks
• The quiz: Chris goes 1 for 2 and disputes the scoring

About the series

Camp Geo is Chris and Jesse's audio textbook version of an introductory Physical Geology course, built for the Camp Geo mobile app, where each lesson comes with a stack of ima