Earth Materials and Surface Processes
Earth Materials and Surface Processes
This domain tests minerals, the three rock classes, weathering and erosion, and the landforms produced by streams, groundwater, glaciers, wind, and mass wasting.
Core concepts
- A mineral is naturally occurring, inorganic, solid, crystalline, and has a definite composition or range. Silicates dominate Earth's crust; Bowen's reaction series predicts crystallization order.
- Igneous texture records cooling: phaneritic (coarse, intrusive), aphanitic (fine, extrusive), porphyritic, vesicular, glassy. Composition ranges from mafic to felsic.
- Sedimentary rocks are clastic (grain size, sorting, rounding), chemical (limestone, rock salt), or organic (coal). Structures include cross-bedding, ripples, and graded bedding.
- Metamorphic rocks are foliated (slate, schist, gneiss) or nonfoliated (quartzite, marble); grade and parent rock matter.
- Weathering breaks rock in place; erosion transports debris. Streams cut V-shaped valleys and build deltas; glaciers carve U-shaped valleys and leave till and erratics; groundwater forms karst; wind builds dunes and loess.
Worked example
A coarse-grained, dark, intrusive rock made mostly of pyroxene and calcium-rich plagioclase is gabbro. Reasoning: coarse crystals mean slow cooling underground; dark mafic minerals indicate mafic composition; the intrusive mafic rock is gabbro, while its extrusive equivalent is basalt.
Traps
Conglomerate has rounded clasts; breccia has angular clasts. Foliation is pressure-driven mineral alignment, not sedimentary bedding. Chemical sedimentary rocks precipitate from solution rather than accumulating as clasts. High-grade metamorphism produces gneiss, not slate. Weathering and erosion are not synonyms.