Earth's Structure, Minerals, and the Rock Cycle
Key terms and concepts on Earth's layers, mineral identification, and the three rock families.
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Questions Covered in This Set
12 cards to master
What are Earth's three compositional layers?
Crust (thin outer skin, granite/basalt), mantle (~2,900 km of dense silicate rock), and core (iron–nickel; liquid outer, solid inner).
Lithosphere vs. asthenosphere
Lithosphere = rigid crust + uppermost solid mantle; it breaks into tectonic plates. Asthenosphere = weak, partly plastic upper mantle that the plates slide on. These are physical (behavior) layers, not compositional ones.
How do we know the outer core is liquid?
S-waves (shear waves) travel only through solids and disappear when they reach the outer core, creating an S-wave shadow zone. P-waves pass through but slow down and bend.
What five conditions must something meet to be a mineral?
Naturally occurring, inorganic, solid, definite chemical composition, and an orderly crystal structure. (Steel fails 'natural,' coal fails 'inorganic,' water fails 'solid.')
What is the most common mineral group in Earth's crust?
Silicates — built from the silicon–oxygen tetrahedron (SiO₄) — make up about 90% of the crust by volume; feldspar and quartz dominate.
What is streak and why is it more reliable than color?
Streak is the color of a mineral's powder rubbed on a porcelain plate. Surface color can vary, but streak is consistent — hematite looks silvery-black but always streaks reddish-brown.
Cleavage vs. fracture
Cleavage is breakage along flat, smooth planes (mica splits into sheets); fracture is irregular breakage (quartz shows curved, shell-like conchoidal fracture).
What controls crystal size in igneous rock?
Cooling rate. Slow cooling deep underground = intrusive, coarse-grained (granite, gabbro). Fast cooling at the surface = extrusive, fine-grained (basalt), glassy (obsidian), or frothy (pumice).
What are the steps that form sedimentary rock?
Weathering → erosion → deposition → compaction → cementation.
How are clastic sedimentary rocks classified?
By particle size: shale (clay), sandstone (sand), conglomerate (rounded pebbles), breccia (angular fragments).
Useful Mohs hardness landmarks
Fingernail ≈ 2.5, copper penny ≈ 3.5, glass ≈ 5.5, steel file ≈ 6.5. Scale runs from talc (1) to diamond (10).
What is the difference between a mineral and a rock?
A mineral is a single substance with a definite composition and crystal structure; a rock is an aggregate of one or more minerals (granite = quartz + feldspar + mica).
