Classifications (Chapter 2)

Question 1

Phaneritic

Answer 1

Individual crystals are visible (with the naked eye)
Also plutonic or intrusive

Question 2

Aphanitic

Answer 2

Individual crystals are not visible (with the naked eye)
Also volcanic or extrusive

Question 3

Fragmental

Answer 3

Has pieces of pre-existing fragmented rock. Also pyroclastic

Question 4

Equigranular

Answer 4

Grain size is more or less even

Question 5

Porphyritic

Answer 5

Two populations of grain size

Question 6

Seriate

Answer 6

Continuous change in grain size

Question 7

Based on Si02 content, what are the four categories igneous rocks can be categorized as? (In the order of increasing Si02 content)

Answer 7

Ultrabasic, Basic, Intermediate, Acidic

Question 8

What are the two components to igneous nomenclature?

Answer 8

The root name and its qualifier(s)

Question 9

If a root name has two qualifiers, which one is more important?

Answer 9

The qualifier that is closest to the root name

Question 10

What are three types of minerals used in the classification scheme?

Answer 10

Essential minerals
Type minerals
Accessory minerals

Question 11

What is an essential mineral?

Answer 11

A mineral that is required to qualify for the root name

Question 12

What is a type mineral?

Answer 12

A mineral that is used as a qualifier to subdivide the rock name

Question 13

What is an accessory mineral?

Answer 13

Minor minerals that are described but not named.

Question 14

True or False: Can the IUGS classification be used for pyroclastic rocks?

Answer 14

False. The IUGS classification can only be used for phaneritic and aphanitic rocks.

Question 15

What are five common minerals/mineral groups that are in igneous rocks?

Answer 15

Quartz, Plagioclase, Alkali Feldspar, Feldspathoids, Mafics and accessories

Question 16

True or False: Quartz and Feldspathoids cannot co-exist

Answer 16

True. As well as quartz and olivine.

Question 17

What type of rocks are included in the QAT diagram?

Answer 17

Felsic Phaneritic Rocks (Diagram 2.1)

Question 18

What type of rocks are included in the APF diagram?

Answer 18

Alkaline Felsic Phaneritic Rocks (Diagram 2.2)

Question 19

What types of rock do the two corner diagrams include?

Answer 19

1) Basic-ultrabasic / mafic-ultramafic rocks (plag rich) (Diagram 2.3)
2) Ultramafic rocks (>90% mafics) (Diagram 2.4)

Question 20

What is the TAS diagram?

Answer 20

A diagram that uses chemical composition as parameters for classification. Usually used for classifying aphanitic rocks

Question 21

What are four special names for high Mg volcanic rocks?

Answer 21

Picrite, Komatiite, Meimechite, Boninite

Question 22

What does the CIPW norm stand for and what is it?

Answer 22

Cross, Iddings, Pirsson, Washingston.
It is a normative mineralogy calculation that can be used when chemical composition of the whole rock is known.

Question 23

What are some important rocks that aren’t included in the IUGS classification diagrams?

Answer 23

Hypabyssal: diabase
Carbonatites
Lamprophyres
Spilites
Keratophyres

Question 24

Pyroclastic rocks

Answer 24

• “Fire-broken” rocks
• Comes from blocks/bombs, lapilli, or ash
• No phenocrysts, just clasts
• > 75% pyroclasts

Question 25

Name a few pryoclastic-sedimentary transitional rocks

Answer 25

Tuffite
Epivolcaniclastics
Aquagene tuff
Hyalotuff / hyaloclastite