Earth's softest mineral is soapstone, also known as talc. According to the Mohs scale, which rubs minerals against one another to determine relative hardness, talc shows signs of scratching when rubbed by every other mineral.
The composition of talc resembles a pile of sheets that only have a casual connection. When talc undergoes pressure from almost any other solid substance, those sheets separate from one another. The mineral just above talc on the Mohs scale is gypsum. Diamonds sit on the opposite end of the scale, having earned the title of hardest mineral, according to the Mineralogical Society of America.