Ruby and Sapphire Are the Same Mineral
Ruby and sapphire are both corundum — the same mineral, aluminum oxide. The only difference is trace impurities: chromium makes it red, iron and titanium make it blue. Diamond and graphite are both pure carbon, yet one is the hardest natural material and the other crumbles when you write.
The Strunz classification groups minerals by chemistry and crystal structure across nine major classes. Native Elements (gold, silver, diamond), Sulfides (pyrite — "fool's gold"), Oxides (ruby, sapphire), Carbonates (calcite, malachite), and the enormous Silicates class, which makes up 90% of Earth's crust.
Guess "emerald" when the answer is "aquamarine" and they meet immediately — both are beryl. Guess "emerald" when the answer is "diamond" and you travel through very different branches. 150 minerals, classified by what they're actually made of.
Did you know?
- *Ruby and sapphire are the same mineral (corundum) — only trace impurities create their different colors.
- *Diamond and graphite are both pure carbon, but diamond forms under extreme pressure deep in Earth's mantle.
- *Quartz is the second most abundant mineral in Earth's crust, found in everything from sand to electronics.
- *Pyrite (fool's gold) is an iron sulfide that was historically used to start fires — the name comes from the Greek word for fire.
- *Feldspar minerals make up roughly 60% of Earth's crust, yet most people have never heard of them.
What is GuessKin?
GuessKin is a free daily guessing game built on real-world taxonomy. Choose from over 20 categories and try to identify the mystery mineral. Each guess reveals how closely related your answer is to the target through a shared classification tree.
How does it work?
Every mineral in GuessKin sits on a taxonomy tree — a branching hierarchy that shows how things are classified and related. When you make a guess, the game shows you the nearest common ancestor between your guess and the answer. The closer that ancestor is to the answer, the warmer you are. The tree visualization grows with each guess, narrowing down where the answer lives and helping you triangulate.
How to get the best score
- •Fewer guesses is better. The ideal game is guessing it in 1. Every guess counts against your score.
- •Speed matters too. The timer starts on your first guess. Quick, confident answers are rewarded.
- •Read the tree. Each guess gives you real taxonomic information. Pay attention to which branch the answer is on and which branches you've already ruled out.
- •Start broad, then narrow. Your first guess splits the tree. Pick something that gives you maximum information, then drill into the revealed branch.
Each GuessKin category uses a real classification system. These aren't made-up groupings — they're the same systems scientists and specialists actually use. New categories are added regularly. Every category is free, with no accounts and no ads.