Engineering geology aspects for design and classification - Tunnel Engineering: Basics and Additional Services for Design and Construction - page 22

and intensity of the processes within the cycle can be very varied, different types of rock
can be formed, which can be categorised into the following rock types:
Igneous rocks, also called pyrogenic or magmatic rocks, are created by magmatic process-
es with the cooling and hardening of molten siliceous flows from the inside of the Earth
(magma). According to O. Wagenbreth [249], the following types can be distinguished:
- Intrusive igneous rocks solidify within the crust and are mostly acidic. Their structure
is fully crystalline and uniformly grained (granite, syenite, diorite, gabbro).
- Hypabyssal igneous rocks penetrate into crevices and solidify as they rise from the inside
of the Earth; their structure is partially similar to intrusive and partially similar to extru-
sive rock (granite-porphyry, syenite-porphyry, diorite-porphyrite, gabbro-porphyrite).
- Extrusive igneous rocks are mostly alkaline and are created when magma exudes onto
the surface of the Earth and solidifies relatively quickly. The structure is thus “porphy-
ritic”, finely crystalline, sometimes even glassy (older extrusive rocks: quartz porphyry,
porphyrite, diabase; younger extrusive rocks: liparite, andesite, basalt).
Figure 2-1 Cycle of rock formation [188].
Sedimentary rocks are created by exogenous dynamic effects (weathering, transport, depo-
sition on land or under the sea) on the surface of the earth. According to the degree of
consolidation, they can be loose sediments, loose rocks or sedimentary rocks. Some rep-
resentatives of this type of rock are listed in Fig 2.1.