the.com/corundum
the second-hardest mineral on Earth, moonlighting as both ruby and sapphire.
same rockRubies and sapphires are identical, just colored differently
hardnessRanks 9 on Mohs, beaten only by diamond
the color trickChromium makes red, iron and titanium make blue
sandpaper jobCrushed into emery for industrial abrasives and grinding
melting pointEndures over 2000 degrees Celsius before liquefying