Descriptive Criteria for Rock (nfm)

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 % 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, 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 descrip-tion of mineral components)

Use standard adjectives, such as shaly, sandy

silty, clayly

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.

texture grain diameter, mm particle name rock name

very fine grained > - 0.1 clay, silt shale, claystone,

siltstone,

limestone

(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, hypidio-morphic 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

3. Discontinuities

a. Joints

(1) Type: bedding, cleavage, foliation, schistosity, extension

(2) Separations: open or closed, how far open

(3) Character of surface: smooth or rough; if rough, how much relief, average asperity angle

(4) Weathering of clay products between surfaces

b. Faults and shear zones

(1) Single plane or zone: how thick

(2) Character of sheared materials in zone

(3) Direction of movement, slicken sides

(4) Clay fillings

c. Solution, cavities, and voids

(1) Size

(2) Shape: planar, irregular, etc.

(3) Orientation (if applicable): developed along joints, bedding planes, at intersections of joints and bedding planes, etc.

(4) Filling: percentage of void volume and type of filling material (e.g. sand, silt, clay, etc.).

Rocks Taxonomy for Construction (nfm)

Igneous Rocks

Color

Principal minerals

Texture

very coarse irregular crystalline

coarse and medium crystalline

fine crystal -line

microcrystalline

glassy

porous

fragmenta

Light

Quartz and feldspar

pegmatite

granite

aplite

Fel -site

rhyolite

pomice

Aah

(fine, loose)

Tuff, (fine cemented)

Breccia (coarse)

cinders (variable)

Felspar, little or no quartz

Syenite

pegmatite

syenite

trachyte

Pitchatose

Intermediate

Feldspar and Mornblende

Diorite Pegmatite

Dio -rite

Dolerite

Andesite

Scoria or vesicular basalt

Dark

Augite and Felspar

Gabbro Pegmatite

Gab -bro

Dia -base

Basalte

Augite, Mornblende, Olivine

Peridolite