Igneous Rocks Texture Quiz

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Questions and Answers

What is the primary textural classification of diorite?

Crystalline

Medium to coarse-grained (correct)

Fine-grained

Porphyritic

Which mineral is NOT commonly found in gabbro?

Olivine

Anorthite

Quartz (correct)

Hornblende

What relationship do the constituents of syenite exhibit?

Porphyritic

Graphic

Inter-grown

All of the above (correct)

In what stage of igneous activity does syenite typically occur?

Plutonic stage Signup and view all the answers

What type of rock is dolerite classified as?

Volcanic basic rock Signup and view all the answers

What makes andesite suitable for use as a decorative building stone?

Its polished blocks Signup and view all the answers

Which of the following is a chief constituent of gabbro?

Feldspar Signup and view all the answers

What is a predominant feature of the mineralogical composition of dolerite?

Presence of calcic plagioclase Signup and view all the answers

What is the primary focus of petrology?

The classification and origin of rocks Signup and view all the answers

Which statement best describes a rock?

A naturally occurring solid aggregate of minerals or organic material Signup and view all the answers

What distinguishes a mineraloid from a mineral?

Mineraloids lack an ordered atomic structure. Signup and view all the answers

Which is NOT a characteristic of a mineral?

Absence of crystalline structure Signup and view all the answers

What kind of materials can be categorized as organic?

Any substance that was alive and is now in or on the soil Signup and view all the answers

What is the significance of studying petrology in engineering?

It provides insight into the properties and behavior of rocks used in construction. Signup and view all the answers

Which of the following is considered a defining characteristic of all minerals?

They possess a specific crystal form and structure. Signup and view all the answers

Which of the following best describes mineraloids?

Mineraloids lack the ordered atomic structure of minerals. Signup and view all the answers

Which igneous rocks are considered most suitable for construction due to their high crushing strength?

Granites, syenites, and dolerites Signup and view all the answers

For what type of structures are basalts recommended?

Roads and foundations Signup and view all the answers

What characteristic defines lamprophyres in terms of their texture?

They are coarse grained and mostly inequigranular. Signup and view all the answers

Where do lamprophyres typically occur?

In fissures and cracks of existing rocks. Signup and view all the answers

Which mineral is NOT typically found in granite?

Plagioclase Signup and view all the answers

What texture can granite exhibit?

Porphyritic and intergrowth Signup and view all the answers

What type of rock do peridotites typically replace in construction due to their appearance?

Basalt and dolerite. Signup and view all the answers

What is a common feature of peridotites regarding their occurrence?

They are typically found as sills and dykes at deeper depths. Signup and view all the answers

What contributes to the colour variation in granites?

Presence of feldspar Signup and view all the answers

Which minerals are commonly extracted from peridotites?

Olivine and augite. Signup and view all the answers

Which of the following statements about diorite is true?

It is typically rich in plagioclase of the sodic group. Signup and view all the answers

Which igneous rocks can provide information about the Earth's mantle compositions?

Peridotites and pegmatites Signup and view all the answers

What is a characteristic feature of diorite's texture?

Coarse- to medium-grained Signup and view all the answers

What is the primary process through which igneous rocks are formed?

Cooling and solidification of magma Signup and view all the answers

Which type of igneous rock is formed from magma that cools and crystallizes within the Earth's crust?

Intrusive igneous rocks Signup and view all the answers

What characteristic texture do igneous rocks typically have?

Interlocking crystalline Signup and view all the answers

Extrusive igneous rocks are formed from magma that becomes what before solidification?

Erupted as lava Signup and view all the answers

Which of the following is an example of intrusive igneous rock?

Granite Signup and view all the answers

How does the rate of cooling affect the texture of igneous rocks?

Slower cooling leads to coarser textures Signup and view all the answers

What distinguishes an intrusive igneous rock from an extrusive one?

Intrusive rocks form below the Earth's surface Signup and view all the answers

What happens to magma during the formation of extrusive igneous rocks?

It erupts and cools quickly above ground Signup and view all the answers

Which of these correctly categorizes igneous rocks based on mode of occurrence?

Intrusive and extrusive Signup and view all the answers

Which characteristic is true for extrusive igneous rocks?

They typically have a fine-grained texture Signup and view all the answers

Study Notes

Igneous Rocks Overview

Igneous rocks are formed from the cooling and solidification of molten material, or magma.
Classified into two categories: intrusive (formed underground) and extrusive (formed above ground).
Commonly used in construction due to high strength, particularly granites, syenites, and dolerites.

Diorite

Generally coarse- to medium-grained with an inequigranular texture.
Characterized by a holocrystalline arrangement of minerals, predominantly plagioclase feldspar.
Quartz is usually absent but may be present as quartz-diorite.
Used in construction and as decorative stones.

Syenite

Displays coarse- to medium-grained and holocrystalline textures.
Can show a graphic or porphyritic relationship among mineral constituents.
Typically forms when magma cools during the plutonic stage of igneous activity.
Applied in construction and mineral extraction of nephaline.

Andesite

Abundant volcanic rock, second in prevalence to basalts.
Occurs as crystallized lava flows; ideal for decorative construction stone and paint industry.

Gabbro and Dolerite

Gabbro is a plutonic basic rock rich in plagioclase feldspars like labradorite and anorthite, along with mafic minerals (augite, hornblende).
Dolerite is a hypabyssal volcanic rock, primarily made of calcic plagioclase and dark minerals such as augite and olivine.

Petrology

Branch of geology focusing on rock formation, classification, and occurrence.
Rock is defined as naturally occurring solid aggregates of minerals, mineraloids, or organic material.

Mineralogical Definitions

Mineral: Naturally occurring inorganic substance with a defined internal structure and chemical composition.
Mineraloid: Solid that resembles a mineral but lacks ordered atomic structure; may have indefinite chemical composition.
Organic Material: Remains of living organisms included in geological contexts.

Igneous Rock Textures

Intrusive igneous rocks have coarse textures due to slower cooling rates within the Earth.
Extrusive rocks cool quickly, resulting in fine-grained textures and interlocking crystalline structures.

Economic Importance

Many igneous rocks, such as peridotites and pegmatites, contain valuable minerals offering economic benefits.
Correct selection of igneous rocks is crucial for construction purposes, such as for tunnels, foundations, and structural work.

Characteristics of Specific Igneous Rocks

Granite: Composed mainly of quartz and feldspar. Shows diverse colors based on feldspar type.
Lamprophyre: Coarse-grained, forms in existing igneous/metamorphic rock fissures.
Peridotite: Typically coarse-grained, found in sills and dykes, valued for its mineral content.

Applications

Andesite and syenite are used in construction as decorative stones.
Gabbro is utilized for its strength in structural applications.

Occurrence Overview

Igneous rocks can occur as surface flows or intrusions, affecting their texture and mineral composition.

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Description

Test your knowledge on the textures of igneous rocks such as diorite and syenite. Explore different arrangements and grain sizes of mineral grains as you answer this quiz. Improve your understanding of holocrystalline and ineguigranular textures!