Final answer:
The softest known mineral that flakes easily when scratched with a fingernail is talc, ranking as the softest on the Mohs' scale of mineral hardness and used in products like baby powder.
Step-by-step explanation:
The softest known mineral that can easily flake when scratched with a fingernail is talc. Talc is composed of hydrated magnesium silicate and is so soft that it can be scratched by a fingernail. It ranks as the softest mineral on the Mohs' scale of mineral hardness, which is a qualitative scale that describes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material.
Talc is commonly used in a variety of products, including baby powder and as a filler in cosmetics. The softness of talc is a defining characteristic, exemplifying how the mineral's physical properties can be easily identified with simple tests such as the fingernail scratch test.