Leptosols are by far the most extensive group of soils in the world. They are found mainly in mountainous regions and in areas where soil has been eroded to the extent that hard rock comes near to the surface. Other (minor) occurrences are along rivers where gravely deposits have accumulated without substantial admixture of fine earth material.
Soils which are either limited in depth by continuous hard rock within 25 cm from the soil surface, or overly mayerial with a calcium carbonate equivalent of more than 40 percent within 25 cm from the soil surface, or contain less than 10 percent (by weight) fine earth (mineral soil material with a diameter of 2 mm or less) to a depth of 75 cm from the soil surface. Leptosols have no diagnostic horizons other than a mollic, ochric, umbric, vertic or yermic horizon.