TM 5-818-1 / AFM 88-3, Chap. 7
Table 2-6. Descriptive Criteria for Rock-Continued
Texture
Grain Diameter, mm
Particle Name
Rock Name
Very fine grained
> - 0.1
Clay, Silt
Shale, Claystone,
Siltstone,
(2) Igneous and metamorphic rocks
Texture
Grain Diameter, mm
Coarse grained
>-5
Medium grained
1-5
Fine grained
0.1 - 1
Aphanite
< 0.1
(3) Textural adjectives. Use simple standard textural adjectives such as porphyritic, vesicular, pegmatitic, granular,
and grains well developed. Do not use sophisticated terms such as holohyaline, hypidiomorphic granular, crystaloblastic,
and cataclastic.
2.
Rock structure
a. Bedding
(1)
Massive: >3 ft thick
(2)
Thick bedded: beds from 1 to 3 ft thick
(3)
Medium bedded: beds from 4 in. to 1 ft thick
(4)
Thin bedded: beds less than 4 in. thick
b. Degree of fracturing (jointing)
(1)
Unfractured: fracture spacing greater than 6 ft
(2)
Slightly fractured: fracture spacing from 3 to 6 ft
(3)
Moderately fractured: fracture spacing from 1 to 3 ft
(4)
Highly fractured: fracture spacing from 4 in. to 1 ft
(5)
Intensely fractured: fracture spacing less than 4 in.
c. Shape of rock blocks
(1)
Blocky: nearly equidimensional
(2)
Elongated: rod-like
(3)
Tabular: flat or bladed
(Continued)
(Sheet 2 of 3)
2-12
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