Introduction to Rocks and Minerals

Rock

A solid aggregate or mass composed of one or more minerals or other materials.

Mineral

A naturally occurring, inorganic solid with a specific chemical composition and an ordered internal structure.

Crystal Form

The geometric shape that a mineral's crystal grows into, reflecting its internal arrangement of atoms.

Cleavage

The tendency of a mineral to break along flat, even surfaces due to its internal structure.

Fracture

The manner in which a mineral breaks when it does not exhibit cleavage, resulting in irregular surfaces.

Luster

The way light interacts with the surface of a mineral, which can be described as metallic, glassy, dull, etc.

Saturation

The point at which a solvent can no longer dissolve additional solute, leading to the formation of solid minerals.

Polymorphs

Materials that share the same chemical composition but have different crystal structures and properties.

Silicate Tetrahedron

A molecular ion consisting of one silicon atom bonded to four oxygen atoms, forming the basis of silicate minerals.

Igneous Rock

Rock formed through the cooling and solidification of molten magma or lava.

Intrusive Rock

Igneous rock that forms from magma cooling slowly beneath the Earth's surface, resulting in larger crystals.

Extrusive Rock

Igneous rock that forms from lava cooling quickly at or near the Earth's surface, resulting in smaller crystals.

Phaneritic Texture

A texture of igneous rock where the crystals are large enough to be seen with the naked eye, typical of intrusive rocks.

Aphanitic Texture

A texture of igneous rock characterized by small, fine-grained crystals that are not visible without magnification.

Vesicular

A texture of igneous rock that contains gas bubbles, resulting in a porous appearance.

Covalent Bonds

A type of chemical bond where atoms share electrons, resulting in a strong bond.

Ionic Bonds

A type of chemical bond formed through the transfer of electrons from one atom to another, resulting in a weaker bond.

Ferromagnesium

A term used to describe minerals that contain iron and magnesium, typically found in oceanic crust.

Non-Ferromagnesium

Minerals that do not contain significant amounts of iron and magnesium, often found in continental crust.

Mica

A group of sheet silicate minerals characterized by their layered structure, allowing them to be split into thin sheets.

Olivine

A mineral that is a primary component of mantle rock, known for its high magnesium and iron content.

Felsic

A type of igneous rock that is rich in silica and has a low iron and magnesium content, often light in color. Has a lower melting point

Mafic

A type of igneous rock that is rich in iron and magnesium, typically darker in color and denser than felsic rocks. Has a higher melting point

Porphyritic

A texture in igneous rocks characterized by large crystals embedded in a finer-grained matrix.

Crystal Habit

The characteristic shape of a mineral's crystals, which can vary based on environmental conditions during growth.

Elasticity

The ability of a mineral to return to its original shape after being deformed.

Diaphaneity

The degree to which a mineral transmits light, categorized as transparent, translucent, or opaque.

Refractive Index

A measure of how much light is bent, or refracted, as it passes through a mineral.

Color of mafic rocks

Dark; black/green

Color of felsic rocks

Light; pink/white

Phaneritic Texture Examples

Granite, Diorite, Gabbro

Aphanitic Texture Examples

Rhyolite, Basalt

Porphoryitic Texture Examples

Andesite

Glassy Texture Examples

Obsidian

Si:O Ratio Importance

it controls the melting temperature, mineral structure, and susceptibility to chemical weathering

Si:O Ratios

As the ratio increases, the melting temperature decreases; As the ratio increases, so does the ability to weather