Geoscience Reference
In-Depth Information
Table 4.11 Contd...
Lithologic discontinuity
There is no norm for characterizing a lithologic
discontinuity. We refer to the rapidity of
textural change, contrasting sand sizes,
the nature of the coarse fragments, the presence
of a 'stone line', the weathering stage of the
coarse fragments…
n value
n = (A - 0.2R)/(C + 3H)
where:
A = water content (%) in the soil in field
condition, calculated on dry soil basis
R = silt % plus sand %
C = clay %
H = organic matter %
If n exceeds 1, the soil can flow between the
fingers when wet, cattle find it difficult to graze
there and after drainage the soil collapses;
below n = 0.7, there is no problem
Petroferric contact
(Gr. petra = rock), contact with an indurated
ferruginous horizon that contains no organic
matter, a feature that distinguishes it from
ortstein (Table 4.11)
Plinthite
Plinth
(Gr. plinthos = brick), horizon rich in iron, clay
and quartz, rust-coloured, formed in wet
environment and which has the property of
becoming hard when dried
Resistant minerals
Such as quartz, sphene, rutile, zircon, tourmaline,
beryl
Slickensides
Polished and often grooved surfaces of clods;
pressure face and slip surface at the same time
Spodic materials
Rich in materials extractable by oxalic acid; pH
< 5.9, reddish or blackish, cemented by organic
matter and aluminium, with or without iron
Volcanic glass
Optically isotropic translucent glass or pumice
Weatherable minerals
Minerals whose resistance to weathering is
intermediate between that of resistant minerals
(1/1 clay minerals, quartz) and that of labile
minerals such as calcite; could be 2/1 clay
minerals (except aluminous chlorite), sepiolite,
talc, glauconite, feldspars, ferromagnesian
minerals, glasses, micas, zeolites and apatite
 
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