Vitric properties (WRB)

Vitric properties is one of the diagnostic properties used, in the WRB system, to discriminate some soils from others.

Description

The term "Vitric properties" (from Latin vitrum, glass) refers to layers with volcanic glass and other primary minerals derived from volcanic ejecta and which contain a limited amount of short-range-order minerals or organo-metallic complexes.

Criteria

Vitric properties :

• require 5 percent or more (by grain count) volcanic glass, glassy aggregates and other glass-coated primary minerals, in the fraction between 0.05 and 2 mm, or in the fraction between 0.02 and 0.25 mm

and :

• require an Al_ox + ½Fe_ox value of 0.4 percent or more

and :

• require a phosphate retention of 25 percent or more

and :

• do not meet one or more of the criteria of the andic properties

and :

• require less than 25 percent (by mass) organic carbon

Field identification

Vitric properties can occur in a surface layer. However, they can also occur under some tens of centimetres of recent pyroclastic deposits. Layers with vitric properties can have an appreciable amount of organic matter. The sand and coarse silt fractions of layers with vitric properties have a significant amount of unaltered or partially altered volcanic glass, glassy aggregates and other glass-coated primary minerals (coarser fractions may be checked by ×10 hand-lens ; finer fractions may be checked by microscope).

Relationships with some diagnostic horizons, properties and materials

Vitric properties are, on the one hand, closely linked with andic properties, into which they may eventually develop. On the other hand, layers with vitric properties develop from tephric materials. Mollic and umbric horizons may exhibit vitric properties as well.

See also

• The FAO reference text, (2007 version)