Rocks Flashcards
(19 cards)
What are the three main types of rocks?
Igneous (from cooled magma/lava)
Sedimentary (from accumulated sediments)
Metamorphic (from altered pre-existing rocks)
How are igneous rocks classified based on cooling rate?
Intrusive (Plutonic): Slow cooling → coarse-grained (e.g., granite).
Extrusive (Volcanic): Rapid cooling → fine-grained (e.g., basalt).
What determines the texture of igneous rocks?
Cooling rate: Slow = phaneritic (visible crystals), fast = aphanitic (microscopic crystals).
Gas bubbles: Vesicular (e.g., pumice).
Name two felsic and two mafic igneous rocks.
Felsic: Granite (intrusive), Rhyolite (extrusive).
Mafic: Gabbro (intrusive), Basalt (extrusive).
What are pyroclastic igneous rocks?
Fragmental rocks from explosive eruptions (e.g., tuff, volcanic breccia).
How are sedimentary rocks classified?
Clastic (fragments: conglomerate, sandstone).
Chemical (precipitates: limestone, evaporites).
Biochemical (organic remains: coal, chert).
What does grain size indicate in clastic sedimentary rocks?
Large grains (gravel): High-energy environments (rivers).
Small grains (clay): Low-energy environments (lakes).
Define “sorting” and “roundness” in sediments.
Sorting: Uniformity of grain size (well-sorted = distant transport).
Roundness: Smoothness of edges (rounded = long transport).
What is lithification?
Process of sediment turning into rock via compaction and cementation.
Name a chemical sedimentary rock and its formation process.
Forms from calcite precipitation (e.g., stalactites) or shell accumulation.
What is metamorphism?
Transformation of rocks by heat, pressure, or fluids without melting.
How are metamorphic rocks classified by texture?
Foliated: Layered (e.g., slate, schist, gneiss).
Non-foliated: Massive (e.g., marble, quartzite).
What is the protolith of marble and quartzite?
Marble: Limestone.
Quartzite: Sandstone.
Describe the metamorphic gradient from shale.
Shale → Slate → Phyllite → Schist → Gneiss → Migmatite (increasing grade)
What are contact vs. regional metamorphism?
Contact: Local, near magma (e.g., hornfels).
Regional: Large-scale, tectonic forces (e.g., schist).
What economic minerals form in metamorphic rocks?
Talc, asbestos (ultramafic protolith).
Graphite (coal protolith).
Gemstones (e.g., ruby, sapphire).
What is the rock cycle?
Continuous process of rock transformation via weathering, melting, and metamorphism.
How does a conglomerate differ from breccia?
Conglomerate: Rounded clasts (long transport).
Breccia: Angular clasts (short transport).
What mineral indicates a high-grade metamorphic rock?
Garnet or sillimanite.
