Characteristics of Geologic Materials and Formations - Geotechnical Engineering Investigation - page 346

TABLE 5.6
Classification of Igneous Rocks a

Minerals b Light-colored rocks

Ortho- clase
feldspar
BHP
With Q

Medium-colored Dark-colored rocks

Ortho- or Plagio-
clase feldspar

Plagio-
clase

No feld-
spar

Plagioclase

BHP BHP HBP

PHOA OPHBA

Grain size Without Q With Q Without Q With Q Without Q Without Q No Q

Pegmatite
Granite

Coarse >1 mm

Phanerites
Equigranular
> 1 mm

Grano-
diorite

Monzonite Tonalite

(quartz
diorite)

Diorite Gabbro Peridotite

Pyroxenite
Dunite (0)

Granite Syenite

Micro-
phanerites
Equigranular
< 1 mm

Aplite Micro-

syenite

Micro-
grano-
diorite

Micro-
monzomite

Micro-
tonalite

Micro-
diorite

Dolerite
(diabase)

Porphyries All phanerites are found with phenocrysts (granite porphyry, etc.)

Aphanites
and
aphanite
porphyries
Classes

Trachyte Quartz,
latite
Felsite (and felsophyre)
Obsidian and pitchstone

Latite

Rhyolite Dacite Andesite

Basalt

Scoria

Vesicular
basalt

Pumice

Porous

Note: Plutonic rocks, Volcanic rocks, Border rocks

a

After Pirsson, L.V. and Knopf, A., Rocks and Rook Minerals , Wiley, New York, 1955. Reprinted with permission
of Wiley. (Excludes pyroclastic rocks.)

b

Minerals: A augite, B biotite. H hornblende, P pyroxene, O olivine, O quartz.

100%

Alkali-feldspar

80%

60%

FIGURE 5.2
Minerals composing the important
igneous rocks. (From Pirsson, L.V.
and Knopf, A., Rocks and Rock Minerals,
Wiley, New York, 1955. Reprinted with
permission of Wiley.)

40%

20%

0%

Texture
Intrusives and lavas are grouped as follows:

Phanerocrystalline (phanerites) have individual grains large enough to be distin-
guished by the unaided eye and are classified by grain size:
Coarse-grained —

●

5 mm diameter (pea size)
Medium-grained — 1 to 5 mm diameter
Fine-grained — 1 mm diameter