Chapter 1 — Introduction to Geology¶
Geology is the study of the Earth — its materials, its structure, and the processes that change it. For the engineer the value is direct: every foundation, cut and tunnel is an intervention in a geological system, and the ground's history explains its present properties.
1.1 What geology covers¶
- Materials — minerals, rocks, and the unconsolidated sediments derived from them.
- Structure — how rock bodies are layered, folded, fractured and faulted.
- Processes — the internal (tectonic, igneous, metamorphic) and external (weathering, erosion, deposition) processes that form and destroy rock.
- Time — geological time is long; the ground the engineer meets is the accumulated result of it.
1.2 Minerals and rocks — the essential distinction¶
A mineral is a naturally occurring substance with a specific chemical composition and an ordered internal structure. A rock is a mixture of one or more minerals. Feldspar, quartz, mica, calcite and halite are minerals; granite, basalt, sandstone, limestone and schist are rocks.
Figure. A close-up of granite and its minerals: H = hornblende, Q = quartz, F = feldspar. Crystals range from about 0.1 to 3 mm. © Steven Earle, CC BY 4.0 — Physical Geology, 2nd ed., Fig. 1.4.2.
1.3 The three rock families¶
- Igneous — solidified from magma or lava. Intrusive (granite) cools slowly at depth and is coarse-grained; extrusive (basalt) cools quickly at the surface and is fine-grained.
- Sedimentary — formed from deposited and then buried sediment. Classified as clastic (by grain size) or chemical/organic.
- Metamorphic — formed from existing rock under heat and pressure; develops foliation.
Key points for the geotechnical engineer¶
- Mineral ≠ rock. A rock's behaviour depends on its mineral assemblage and its structure, not on its name alone.
- Rock names describe genesis, not engineering performance — two granites can behave quite differently.
- The rock cycle means any rock can be the parent of the soil above it.
Terminology¶
| English | Vietnamese |
|---|---|
| geology | địa chất học |
| mineral | khoáng vật |
| rock | đá |
| igneous / sedimentary / metamorphic | magma / trầm tích / biến chất |
| intrusive / extrusive | xâm nhập / phun trào |
| rock cycle | vòng tuần hoàn đá |
Digest of Chapter 1, Physical Geology – 2nd Edition, by Steven Earle (CC BY 4.0).