Geology Midterm Review: Density, Plate Tectonics, Minerals, and Rocks

Comprehensive vocabulary flashcard set reviewing Earth layers, isostasy, plate tectonic boundaries, mineral physical properties, igneous compositions and textures, and metamorphic processes.

Density

The physical property defined by the formula $\text{Density} = \frac{\text{mass}}{\text{volume}}$, which governs whether materials sink or float.

Isostatic Equilibrium

The balance and ratio of percentage above and below a surface for a floating object, where variations in density dictate how much it sinks or floats.

Continental Crust

The thicker, less dense layer of Earth's crust, commonly composed of granite, which sits at a higher elevation.

Oceanic Crust

The thinner, medium-dense crustal layer primarily composed of basalt, residing at a lower elevation than continental crust.

Mantle

The densest underlying layer beneath the crust, predominantly composed of peridotite.

Convergent Boundary

A plate boundary where tectonic plates collide, characterized by asymmetric shallow-to-deep earthquakes, volcanic activity, mountain formation, and ocean trenches created via subduction.

Divergent Boundary

A plate boundary where tectonic plates pull apart, generating ocean ridges, symmetric shallow earthquakes, volcanic activity, and the symmetric formation of new oceanic crust.

Transform Boundary

A plate boundary where tectonic plates slide horizontally past one another, characterized by symmetric shallow earthquakes.

Subduction Zone

A convergent boundary setting where an oceanic plate bends and plunges beneath another plate into the mantle, resulting in deep trenches, crust melting, volcanic arcs, and shallow-to-deep earthquakes.

Mariana Trench

The deepest oceanic trench on Earth, plunging more than $35{,}000\text{ feet}$ below sea level where an oceanic plate subducts.

Luster

A mineral identification property describing how light reflects off its surface, broadly categorized as metallic or nonmetallic.

Streak

The color of a mineral in its powdered form, observed by rubbing the mineral specimen across an unglazed porcelain streak plate.

Cleavage vs. Fracture

Cleavage is the tendency of a mineral to break smoothly along flat crystal planes, whereas fracture is breakage along irregular, non-planar surfaces.

Mohs Hardness Reference Scale

A diagnostic scale comparing mineral scratch resistance against common objects: Fingernail ($2.5$), Penny ($3.5$), Glass plate ($5.5$), and Steel nail ($6.5$).

Felsic Composition

An igneous chemical classification characterized by minerals rich in silica and light coloration (white, clear, pink). Examples include granite, rhyolite, obsidian, and pumice.

Intermediate Composition

An igneous chemical composition containing less silica than felsic rocks—approximately half felsic and half mafic minerals, resulting in a black-and-white or gray appearance (e.g., diorite, andesite).

Mafic Composition

An igneous composition rich in minerals with low silica content, displaying dark colors such as black, dark gray, or gray. Examples include gabbro, basalt, and scoria.

Ultramafic Composition

An igneous composition with relatively no silica that is characteristically green, dominated by olivine and pyroxene (e.g., peridotite).

Intrusive (Plutonic) Rocks

Igneous rocks that cool and solidify slowly inside the Earth, including granite, diorite, gabbro, and peridotite.

Phaneritic Texture

A coarse-grained igneous texture in which individual mineral grains are large enough to be seen with the unaided eye, formed via slow subsurface cooling.

Extrusive (Volcanic) Rocks

Igneous rocks formed by magma erupting as lava and cooling rapidly on Earth's surface, such as rhyolite, basalt, obsidian, pumice, and scoria.

Aphanitic Texture

A fine-grained igneous texture where individual mineral grains cannot be seen without magnification, resulting from rapid cooling at the surface.

Vesicular Texture

An extrusive igneous texture characterized by numerous cavities or holes created by gas bubbles escaping from cooling lava (e.g., pumice, scoria).

Obsidian

A dark, extrusive volcanic rock displaying a glassy texture produced by the rapid cooling of silica-rich lava on Earth's surface.

Pumice

A light-colored, felsic extrusive igneous rock exhibiting a highly vesicular texture filled with holes.

Scoria

A dark-colored, mafic extrusive igneous rock featuring a vesicular texture with prominent holes.

Protolith

The original parent rock from which a metamorphic rock is derived prior to being altered by heat and pressure.

Foliated Metamorphic Rocks

Metamorphic rocks characterized by a planar arrangement of mineral grains appearing as banding or layering, produced by regional pressure and heat (e.g., slate, phyllite, schist, gneiss).

Non-foliated Metamorphic Rocks

Metamorphic rocks lacking a banded or layered texture, typically formed through contact metamorphism driven primarily by intense heat (e.g., marble, quartzite, serpentinite).

Serpentinite

A green, non-foliated metamorphic rock lacking banding, produced through contact metamorphism.

Regional Metamorphism

Metamorphism resulting from large-scale increases in both temperature and directed pressure along convergent plate boundaries and mountain belts, forming foliated textures.

Contact Metamorphism

Metamorphism primarily driven by high thermal energy directly adjacent to magma chambers or igneous intrusions, creating non-foliated rocks without directional pressure.