Igneous Textures Quiz

Questions and Answers

What is the definition of Texture in the context of igneous rocks?

The age of a rock

The size, shape, and arrangement of mineral grains or crystals in a rock (correct)

The color of a rock

The hardness of a rock

What is glass in the context of igneous rocks?

Rock that consists of unordered ions.

What does aphanitic mean?

Igneous rocks that form at the surface or as small masses within the upper crust where cooling is relatively rapid, possessing a very fine-grained texture.

Rocks that contain spherical or elongated openings are said to have ______ texture.

vesicular Signup and view all the answers

What does phaneritic mean?

Igneous rocks that form when magma slowly crystallizes at depth have this texture. Signup and view all the answers

What is porphyritic texture?

An igneous texture consisting of large crystals embedded in a matrix of much smaller crystals. Signup and view all the answers

What are phenocrysts?

The large crystals in a porphyritic rock. Signup and view all the answers

What is glassy texture?

A term used to describe the texture of certain igneous rocks, such as obsidian, that contain no crystals. Signup and view all the answers

What does pyroclastic mean?

An igneous rock texture resulting from the consolidation of individual rock fragments that are ejected during a violent volcanic eruption. Signup and view all the answers

What is fragmental texture?

Rocks with a fragmental texture consist of igneous fragments that are packed together, welded together, or cemented together after having solidified. Signup and view all the answers

What are pegmatites?

Exceptionally coarse-grained igneous rocks. Signup and view all the answers

What does pegmatitic texture indicate?

Exceptionally coarse-grained igneous rocks exhibit this texture. Signup and view all the answers

Study Notes

Igneous Textures

Texture: Refers to the size, shape, and arrangement of mineral grains or crystals in igneous rocks.
Glass: Describes rock made of unordered ions, lacking a crystalline structure.
Aphanitic Texture: Characterizes igneous rocks formed at the surface or near the upper crust with rapid cooling, resulting in a very fine-grained appearance.
Vesicular Texture: Identified by the presence of vesicles, which are spherical or elongated openings within the rock.
Phaneritic Texture: Found in igneous rocks that crystallize slowly at depth, showing a coarse-grained texture with visible crystals.
Porphyritic Texture: Features large crystals known as phenocrysts embedded in a matrix of much smaller crystals, indicating different cooling rates.
Phenocrysts: The term for large crystals that stand out in a porphyritic rock.
Glassy Texture: Describes the texture of igneous rocks like obsidian, marked by an absence of crystals, giving a smooth, glass-like appearance.
Pyroclastic Texture: Resulting from the consolidation of rock fragments ejected during explosive volcanic eruptions, forming a mixed-texture rock.
Fragmental Texture: Comprises igneous fragments that have solidified and can be packed, welded, or cemented together.
Pegmatites: Notable for their exceptionally coarse-grained structure, typically formed in the late stages of magma crystallization.
Pegmatitic Texture: Used to describe the very large crystals present in pegmatites, signifying an environment of slow cooling and crystallization.

Description

Test your knowledge on the various textures of igneous rocks. This quiz covers key definitions and characteristics such as aphanitic, vesicular, phaneritic, and porphyritic textures. Deepen your understanding of how cooling rates affect crystal formation in igneous geology.