TM 5-818-1 / AFM 88-3, Chap. 7
Table 2-6. Descriptive Criter for Rock
a. Rock name (Generic)
Very soft: can be deformed by hand
Soft: can be scratched with a fingernail
Moderately hard: can be scratched easily with a knife
Hard: can be scratched with difficulty with a knife
Very hard: cannot be scratched with a knife
c. Degree of weathering
Unweathered: no evidence of any mechanical or chemical alteration.
Slightly weathered: slight discoloration on surface, slight alteration along discontinuities, less than 10
percent of the rock volume altered, and strength substantially unaffected.
Moderately weathered: discoloring evident, surface pitted and altered with alteration penetrating well
below rock surfaces, weathering "halos" evident, 10 to 50 percent of the rock altered, and strength
noticeably less than fresh rock.
Highly weathered: entire mass discolored, alteration in nearly all of the rock with some pockets of slightly
weathered rock noticeable, some minerals leached away, and only a fraction of original strength (with wet strength usually
lower than dry strength) retained.
Decomposed: rock reduced to a soil with relect rock texture (saprolite) and generally molded and
crumbled by hand.
d. Lithology (macro description of mineral components). Use standard adjectives, such as shaly, sandy, silty,
and calcareous. Note inclusions, concretions, nodules, etc.
e. Texture and grain size
Grain Diameter, mm
< - 80
5 -. 80
0.4 - 2
0.1 - 0.4
* Use clay-sand texture to describe conglomerate matrix.
(Sheet 1 of 3)