Teaching Volcanic Petrology in Limited Time

Jim Nicholls: Calgary, Alberta, Canadahttp://www.gtwist.ca

The Mineralogical Sciences:Endangered topics in geoscience curricula

One Contributing Factor

Students specialize as undergraduates:Petroleum geologists,Environmental geoscientists,Geophysicists,Etc.

Why Did This Happen?

Created courses labeled Rocks and Minerals or Earth Materials or something similar.

Learning Objective like: Students will develop the ability to Identify Rocks and Minerals

How has specialization been accommodated?

Mineral Science is more than identifying rocks and minerals!

• Crystallography• Mineralogy• Geochemistry• Petrology• Optics and Diffractometry• The list goes on and on …

BUT

Ask a Couple of Critical Questions

Why should any geoscientist know something about the mineral sciences?

What should they know about the mineral sciences?

Depends on topic, but put everything on the table.Justify all content. Example: Volcanic Petrology.

Geoscience is a profession with a focus on the Earth. Mineral sciences are part of that focus; any geoscientist should know something about them.

Geoscientists Should be Able Read, Understand, and Review the Popular

Literature

What’s written about igneous rocks in the popular literature?

• Geoscientific context: Extensive, done well.• Stories are nearly always about volcanoes and

volcanic phenomena.• Rock names: few, simple, unused or

undefined.• Textures: names seldom used or described.

What to Leave Out?

• Plutonic rocks

• Rock names• Texture names

Leaving this one out really sucks!

(Well, almost)

What to Include (1)

• Geoscientific context No more Rocks in Boxes• Descriptions of textures

o Fragmental rocks (Explosive eruptions)o Flow rocks (Quiet eruptions)o Glassy rocks

• Mafic – felsic continuum• Silica content versus Mafic index

What to Include (2)

• Activity of silica• Activity of alumina

Mineral assemblages reflect activities.Activities can be related to chemistry.

• Conceptual model: Activity of sugar in watero Sugar – water solutions provide a physical, conceptual

model (Kitchen stove, refrigerator, freezer).o Taste, stir, poke

• Learning to relate specific mineral assemblages to chemical activities on a relative scale

Using Activity: Challenges• Learning the concept• Applying concept

Minerals and aSiO2

Students recognize whether a few different minerals are either present or absent from a rock.

They can then infer relative activity of SiO2 or Al2O3.

Ultra-low(Very Rare)

Low(Uncommon)

Medium (Common) High(Rare)

Sanidine-LeuciteMg-rich Mafic Minerals

BiotiteCa-pyroxeneOlivine

Unique Accessory Minerals

Wadeite (K2ZrSi3O9)Priderite (KTi8O16)

Mafic MineralsNa-pyroxeneAenigmatiteNa-amphiboles

Felsic MineralsAnorthoclaseQuartz – nephelineDepends on silica activity

No plagioclase

Usual rock-forming minerals:

FeldsparOlivinePyroxeneBiotiteAmphibole

Critical mineral: Topaz otherwise typical felsic mineral assemblages

Minerals and aAl2O3

Rock Space

Rock Space encompasses 90% or more of volcanic rocks on Earth.

Emphasizes the diversity of volcanic rocks on Earth.

Simple to use and easy to learn.

Rock Names

Provide Comfort and Support

The IUGS Classification has 179 root names(Le Maitre, 2002)oMuscovite Granite – a modified nameoGranite – a root name

oBasalt, Andesite, Rhyolite, Obsidian

Rock Names with Comfort and Support

Rhyoli

te

Andes

ite

Basalt

Where, in Rock Space, Does Comfort and Support Fall?

• Rhyolite

• Andesite

• Basalt

• Obsidian

Explosive Eruptions, Craters, Calderas, andActivity of SiO2

Quiet Eruptions, Lava Flows, and Activity of SiO2

Organizational concepts come before facts.

Facts are learned by applying organizational concepts to case studies.

Acknowledgements

• Dr. Paul Hoskin• Dr. Leslie Reid• Mavis Stout• Dr. Frank Brown• Dr. Thure Cerling• Erin Ernst• Colin Rowell• Michelle Speta• Elissa Lynn

A detailed expression of the concepts described here can be down loaded from: http://www.gtwist.ca