MetamorphicDescription describes the character of metamorphism applied to a CompoundMaterial or GeologicUnit using one or more properties including estimated intensity (grade; eg high grade, low grade), characteristic metamorphic mineral assemblages (facies; eg, greenschist, amphibolite), peak P-T estimates, and protolith material if known.
The FabricDescription class describes all types of fabrics associated with a CompoundMaterial (ie, tectonic, metamorphic, sedimentary, igneous fabrics or textures). It denotes a pattern, defined by one or more CompoundMaterial constituents, that is present throughout a rock body when considered at some scale. FabricDescription is defined based on the average configuration of many constituents. Penetrative fabric denotes that these constituents are distributed throughout the rock volume at the scale of observation [Passchier and Trouw, 1998], and are repeated at distances that are small relative to the scale of the whole, such that they can be considered to pervade the whole uniformly (Turner and Weiss [1963] p. 21-24; Hobbs and others [1976], p. 73; Jackson [1997]; Passchier and Trouw [1998]). FabricDescription is distinguished from Particle Geometry based on the criteria that Particle Geometry is preserved if a CompoundMaterial is disaggregated, while FabricDescription is not defined if the material is disaggregated. Use gml:description to capture any free text to indicate any specific or peculiar features of the described fabric in the CompoundMaterial.
AlterationDescription decribes aspects of a geologic unit or earth material that are the result of bulk chemical, mineralogical or physical changes related to change in the physical or chemical environment. Includes weathering, supergene alteration, hydrothermal alteration and metasomatic effects not considered metamorphic. A soil profile description would have to be constructed as a GeologicUnit with unit parts representing the various horizons in the profile. Thickness of a weathering profile can be delivered as unitThickness of an AlterationUnit.
The MaterialRelation class describes the relationships between constituent parts in an Earth Material (eg: A mineral overgrowth on a phenocryst within a granite). Relationships are always binary and directional. There is always a single source and a single target. The relationship is always defined from the perspective of the Source and is generally an active verb. Example: Consider an overgrowth of albite on plagioclase in a granite. The Source would originate with the albite constituentPart description. In this case, the Target would point to the plagioclase constituentPart description and the relationship attribute would be 'overgrowth' and the sourceRole is 'overgrows'. Other appropriate role attributes might include: crosscuts, replaces, etc. for crosscutting and replacement relationships. Inverse relationships must be explicitly recorded as well or else they are invisible.
ParticleGeometryDescription describes particles in a CompoundMaterial independent of their relationship to each other or orientation. It is distinguished from Fabric in that the ParticleGeometryDescription remains constant if the material is disaggregated into its constituent particles, whereas Fabric is lost if the material is disaggregated. Properties include the particle size (grainsize), particle sorting (size distribution, eg: well sorted, poorly sorted, bimodal sorting), particle shape (surface rounding or crystal face development, eg: well rounded, euhedral, anhedral), and particle aspectRatio (eg: elongated, platy, bladed, compact, acicular).