TM 5-818-1 / AFM 88-3, Chap. 7
Table 2-6. Descriptive Criter for Rock
1.
Rock type
a. Rock name (Generic)
b. Hardness
(1)
Very soft: can be deformed by hand
(2)
Soft: can be scratched with a fingernail
(3)
Moderately hard: can be scratched easily with a knife
(4)
Hard: can be scratched with difficulty with a knife
(5)
Very hard: cannot be scratched with a knife
c. Degree of weathering
(1)
Unweathered: no evidence of any mechanical or chemical alteration.
(2)
Slightly weathered: slight discoloration on surface, slight alteration along discontinuities, less than 10
percent of the rock volume altered, and strength substantially unaffected.
(3)
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.
(4)
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.
(5)
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
(1)
Sedimentary rocks
Texture
Grain Diameter, mm
Particle Name
Rock Name
*
< - 80
Cobble
Conglomerate
*
5 -. 80
Gravel
Coarse grained
2-5
Medium grained
0.4 - 2
Sand
Sandstone
Fine grained
0.1 - 0.4
* Use clay-sand texture to describe conglomerate matrix.
(Continued)
(Sheet 1 of 3)
2-11
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