What mineral has the lowest number on the Mohs scale?

The story behind the answer

Talc is the softest mineral on the Mohs hardness scale, assigned a value of 1. It’s easily scratched by all other common minerals because its sheet-like crystal structure has very weak bonds between layers, allowing them to slide—hence talc’s slippery, powdery feel (talcum powder). For context, gypsum is 2, quartz is 7, and diamond is the hardest at 10.

Memory tip: Talc touches skin (talcum powder) so it’s the softest; diamond cuts glass so it’s the hardest. Developed by Friedrich Mohs in 1812, the scale is a quick, relative field test based on what scratches what, not a linear measure of hardness.