Unit 5: Minerals
What actually makes something a mineral, and the handful of physical tests geologists use to identify one out in the field.
4 topics · 13 questions
Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.
What Makes a Mineral a Mineral
- How it worksHow do the five requirements for a mineral sort quartz and salt from everything else around them?
- Common mistakeWhy isn't coal classified as a mineral even though it forms underground like one?
- Going furtherWhat happens to a mineral's classification if the exact same compound is made in a lab instead of forming naturally?
Your turn1 of 2
Table salt is classified as a mineral, but window glass, also a solid made of silicon and oxygen, is not. Why does table salt count as a mineral but the glass in a window does not?Crystal Structure and Atomic Arrangement
- How it worksHow does a repeating, orderly arrangement of atoms force a crystal to grow into flat geometric faces?
- Common mistakeWhy isn't a crystal's outward shape just a random accident of how it happened to cool?
- Ties togetherHow can graphite and diamond, made of the exact same carbon atoms, end up as two totally different minerals?
Your turn1 of 2
Quartz crystals reliably grow with flat faces meeting at sharp, predictable angles, wherever they form. Why does a crystal's outward shape reflect more than a random accident of cooling?Identifying Minerals: Hardness, Streak, Cleavage
- How it worksHow does the Mohs hardness scale rank minerals by which one can scratch which?
- How it worksWalk me through testing an unknown mineral's streak, hardness, and cleavage to identify it.
- Worked exampleFind whether a mineral that scratches glass but is scratched by quartz falls above or below 7 on the Mohs scale.
- Common mistakeWhy isn't a mineral's color a reliable way to identify what it actually is?
Your turn1 of 2
An unknown mineral scratches a mineral with Mohs hardness 5 but is itself scratched by a mineral with Mohs hardness 8. Assuming the unknown mineral's own hardness sits exactly halfway between these two values, what is its Mohs hardness?Silicate vs Nonsilicate Minerals
- How it worksHow does one tetrahedron of silicon and oxygen link into chains, sheets, and frameworks to build different silicate minerals?
- Going furtherWhat group of minerals forms instead of silicates in a rock with almost no silicon or oxygen, like limestone?
- Ties togetherHow does the silicate tetrahedron's shape explain why mica splits into sheets but quartz does not?
Your turn1 of 2
Silicate minerals make up the vast majority of Earth's crust by volume, far outweighing every nonsilicate mineral group combined. Why do silicate minerals make up such a huge share of Earth's crust compared to every other group combined?