Only "living" things can be healthy. So, when we discuss soil health we're talking about a living breathing organism.
Soil is the interface between land, air, organic material, and rock. If you pick up a hand full of soil you'll be holding about 45% rock-based material, 25% Water, 25% Air, and 5% Organic matter or humus.
45% rock-based material or minerals- will be composed of a mixture of sand, clay, silt, and gravel.
25 % Water- all soil has a water holding capacity depending on the soil's composition
25% Air- all life in the soil will depend on the ability of the soil to allow penetration of oxygen
05% Organic material- the mass of both living and non-living carbon sources
Soil is composed primarily of minerals which are produced from parent material (rock) that is weathered or broken into small pieces. Beyond occasional stones, gravel, and other rock debris, most of the mineral particles are called sand, silt, or clay.
Sand, silt, and clay give soil it's texture.
Sand particles range in diameter from 2 mm to 0.05 mm, are easily seen with the unaided eye, and feel gritty. [One millimeter (mm) is about the thickness of a dime.]
Silt particles are between 0.05 mm and 0.002 mm and feel like flour.
Clay particles are smaller than 0.002 mm and cannot be seen with the unaided eye. Clay particles are the most reactive mineral ingredient in the soil. Wet clay usually feels sticky.