Minerals from magma and hot water, soil from broken rock
Most minerals form when magma cools. Silica-, potassium- and sodium-rich magma gives quartz and mica; magnesium- and iron-rich magma gives olivine and pyroxene. Silicates are the commonest mineral group in Earth’s crust. Other minerals form from hot, mineral-rich water at hydrothermal vents on the sea floor: sea water heated by magma, at about 400 °C, meets cold ocean water, about 2 °C, and the dissolved minerals crystallise, as in calcite and apatite. Crystallisation also happens when a solution holds more dissolved material than it can keep, called supersaturation, for example when salt water dries on a sunny windowsill. Soil forms from weathered rock plus humus, with water and air. Weathering breaks rock where it is; erosion moves the pieces. Soil has particles of different sizes: gravel, sand, silt and clay. Transported soil is carried by water or wind: the Nile Delta’s soil came down the Nile from the Ethiopian highlands. Sedentary soil stays where the rock weathered, like the oasis and Mariout soils; and most Egyptian soil is transported soil.
Soil jar and salt dish. Part 1: half-fill a clear jar with garden soil, add water, close it and shake. Leave it for a day and draw the layers. Part 2: dissolve salt in warm tap water in a saucer, place it on a sunny windowsill and look at the crystals with a magnifier after some days. Do not use hot sodium-acetate solutions or heat anything. Describe what you see; do not promise a result.