The soil in Madeira
is of volcanic origin, consisting mainly of basalt,
trachytes and trachydolerites, tufa, scoria (clinker)
Over time, the volcanic rock disintegrates under the
erosion of sun and rain and produces a variety of
soils. In general terms, these soils are clayey, acid,
rich in organic material, magnesium and iron, poor
in potassium and adequate in phosphorus.
predominates at lower altitudes, and is the origin
of more or less clayey dark or reddish-brown soils.
Trachytes are grey or dark-grey rocks found above
300 metres. Trachydolerites are lighter coloured and
are found at very high altitudes. Tufa is solidified
volcanic mud and occurs in two forms: pedra mole,
which is yellow, and cantaria de forno, which
is red. They have a variable composition. Scoria is
solidified cellular lava, dark (sometimes purple)
in colour, and porous in texture. Conglomerates are
formed from basalt and tufa detritus.