Chapter 2 — Minerals¶
Minerals are the building blocks of rock, and a small number of them dominate the Earth's crust. Recognising them is the first practical skill of field geology — and the reason a borehole log can say "weathered granite" rather than "grey stuff".
2.1 What defines a mineral¶
A mineral is naturally occurring, has a definite chemical composition (or a limited range), and has an ordered atomic structure (a lattice). Atoms are held in the lattice by ionic and covalent bonding.
2.2 The silicate minerals¶
Silicates make up the great majority of crustal rock. They are built from the silica tetrahedron (SiO₄), combined in different ways — isolated, chains, sheets, frameworks — and that internal arrangement controls how the mineral behaves, including how it cleaves and how it weathers.
- Framework silicates — quartz, feldspar. Hard, resistant; quartz survives weathering and becomes the sand fraction of soil.
- Sheet silicates — mica, clay minerals, chlorite. Cleave into sheets and are the weak, water-sensitive minerals in soil and rock.
- Chain silicates — amphibole, pyroxene.
2.3 Non-silicate minerals¶
Carbonates (calcite, dolomite), oxides (hematite, magnetite), sulphides, sulphates (gypsum) and halides. Calcite and dolomite matter enormously for foundations because they dissolve, producing karst.
Key points for the geotechnical engineer¶
- Quartz is the survivor. It resists weathering, which is why sand is quartz-rich and why quartz content predicts a granular soil's behaviour.
- Clay minerals come from silicates that did not survive. They are the weathering product of feldspar and mica — and the source of most soil problems.
- Carbonates dissolve. Any rock containing calcite or dolomite can form karst.
- Mineral identification is what makes a field description meaningful and defensible.
Terminology¶
| English | Vietnamese |
|---|---|
| mineral | khoáng vật |
| silicate | khoáng vật silicat |
| quartz | thạch anh |
| feldspar | fenspat |
| mica | mica (mi-ca) |
| clay mineral | khoáng vật sét |
| carbonate / calcite | khoáng vật cacbonat / canxit |
| cleavage | cát khai |
Digest of Chapter 2, Physical Geology – 2nd Edition, by Steven Earle (CC BY 4.0).