Rocks, Minerals, and Surface Processes
Rocks, Minerals, and Surface Processes
This domain tests mineral identification, the rock cycle, weathering and erosion, and how moving water, wind, and ice shape landscapes.
Core rules and concepts
- A mineral is naturally occurring, inorganic, solid, has a definite chemical composition, and an ordered atomic structure. Identify minerals by hardness (Mohs scale), cleavage or fracture, luster, streak, color, density, and crystal form.
- Igneous rocks: intrusive (coarse-grained) versus extrusive (fine-grained); felsic (light, silica-rich) versus mafic (dark, iron-magnesium-rich).
- Sedimentary rocks: clastic, chemical, and organic. Metamorphic rocks: foliated versus nonfoliated.
- Weathering breaks rock physically (frost wedging, exfoliation) or chemically (oxidation, hydrolysis, carbonation). Erosion transports sediment by water, wind, ice, or gravity.
- Stream velocity controls erosion and deposition: larger, denser, rounder particles settle first when velocity drops.
Worked example
A coarse-grained, light-colored igneous rock containing quartz, feldspar, and mica is granite. Its coarse texture means it cooled slowly underground (intrusive), and its light minerals indicate felsic composition. A fine-grained dark rock with the same general setting would be basalt, extrusive and mafic.
Traps that cost marks
- Using color alone to identify a mineral; streak and hardness are more reliable.
- Confusing cleavage (flat planes) with fracture (irregular breakage).
- Calling limestone clastic when it is commonly chemical or organic.
- Assuming rounding means a short transport distance; rounding increases with transport.