KEY TO THE B-FABRICS

Definition: The b-fabric describes the fabric of the fine material (micromass) of the groundmass as deduced from the pattern of interference colors when observed between crossed polarizers. The b-fabrics are excluded from the pedofeatures as only a few of them (within striated types) could fit in the definition of pedofeatures.

Following types are distinguished, using an objective of at least x6 and conoscopic illumination on thin sections of 30mm or thinner.

1. no interference colors are visible: undifferentiated b-fabric

2. the interference colors are due to the presence of joining or overlapping crystallites (e.g. of calcite) or very small mineral fragments (e.g. sericite): crystallitic b-fabric

(Patterns of the arrangement of the crystallites can be described using the terms given for striated b-fabrics. If crystals are not in contact and larger areas of clay are visible between, an intergrade with one of the following types may be described)

3. the micromass exhibits as a whole a preferred parallel orientation (simultaneous extinction or appearance of interference colors): strial b-fabric

3.1. there is one preferred direction: unistrial b-fabric

3.2. there are two preferred directions: bistrial b-fabric

4. the micromass exhibits elongated zones or streaks (so called striations) more than 30 mm long, composed of parallel oriented prolate domains showing more or less simultaneous interference colors: striated b-fabric *

4.1. the striations are arranged parallel to surface of voids: porostriated b-fabric

4.2. the striations are arranged parallel to the surface of grains or other hard bodies: granostriated b-fabric

4.3. the striations are arranged as concentric rings: concentric striated b-fabric

4.4. the striations are arranged in the form of more or less circular features: circular striated b-fabric

4.5. the striations form elongated worm-like features with a crescent-like internal fabric: crescent striated b-fabric

4.6. the striations occur as isolated and interdependent streaks: monostriated b-fabric

4.7. the striations occur as parallel or subparallel sets which do not intersect: parallel striated b-fabric

4.8. the striations occur as two parallel or subparallel sets which intersect: cross striated b-fabric

4.9. other arrangements of striations random striated b-fabric

5. the striations are smaller than 30 mm, randomly oriented and

5.1. are in contact which each other, forming a mosaic-like pattern: mosaic speckled b-fabric

5.2. are isolated: stipple speckled b-fabric

* More than one striated type can be present; therefore return to the key after identification of the dominant type. Complex types are described by enumerating the observed types, putting the most dominant at the end. E.g. random-grano-porostriated means that random striated is the less pronounced type, poro striated the most developed one.

Note: compared to the "Handbook" following alterations have been made: a minimum size of 30 mm was introduced in order to distinguish striated from speckled b-fabrics; reticulate striated b-fabrics were deleted and incorporated in the cross-striated type, as the angle of intersection is a function of the relative orientation of the section.