Mineral & rock ID defense
This is a live exam at the bench. The student is handed a tray of unknown mineral and rock specimens and the tools to test them — a streak plate, a glass plate, a hand lens, and a dropper of dilute acid. They scratch for hardness, drag for streak, look for luster and cleavage, and watch for the fizz that gives away a carbonate — then name each specimen. Then the guide starts asking: why that mineral and not its look-alike, what the streak actually told you, why the acid mattered. There is no key to consult and no photo to match: the student stands over the tray and defends each call out loud.
| Criterion | Not yet | Approaching | Mastered |
|---|---|---|---|
| Streak, hardness & luster | Misreads streak, cannot run a scratch test, or confuses metallic and nonmetallic luster. | Gets streak and luster but applies the Mohs scale loosely or inconsistently. | Reads streak, places hardness on the Mohs scale, and describes luster and color precisely for each specimen. |
| Cleavage, fracture & the acid test | Cannot tell cleavage from fracture, or skips the acid test entirely. | Notices cleavage but miscounts directions, or runs the acid test without reading the result. | Distinguishes cleavage from fracture, counts cleavage directions, and uses the fizz test to flag carbonates. |
| Identification & use of a key | Guesses an identity that the properties do not support. | Reaches a plausible ID but leans on one property instead of the whole set. | Chains streak, hardness, luster, cleavage, and the acid test through a key to a defensible identification. |
| Technique & specimen care | Contaminates the streak plate, mishandles specimens, or crowds the workspace. | Generally careful but reuses a dirty plate or handles the acid loosely. | Keeps plates and tools clean between tests, handles specimens and acid correctly, and works in order. |
| Oral defense under questioning | Folds at the first follow-up or recites a memorized line that does not fit the specimen. | Answers some follow-ups, falters when asked to rule out a look-alike. | Handles unrehearsed follow-ups about this specimen with sound, on-the-spot reasoning. |
“It left a white streak, I couldn’t scratch it with a steel nail but it scratched glass, so it’s around 6 to 7 on Mohs — and it broke along flat faces, not conchoidally. That rules out quartz and points to a feldspar. The acid did nothing, so it’s not a carbonate.”
“It’s shiny and kind of hard, so maybe quartz? I didn’t really check the streak. I’d have to guess between a couple of them.”
This assessment is AI-proof by design: it happens at the bench, with real specimens, a real streak plate, and real acid, in real time. No chatbot can scratch a mineral it cannot hold, watch for a fizz it cannot see, or defend an identification under a follow-up question. Mastery is shown by doing and defending — not by submitting.