Teaching Volcanic Petrology in Limited Time
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Teaching Volcanic Petrology in Limited Time
Jim Nicholls: Calgary, Alberta, Canadahttp://www.gtwist.ca
The Mineralogical Sciences:Endangered topics in geoscience curricula
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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?
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Mineral Science is more than identifying rocks and minerals!
• Crystallography• Mineralogy• Geochemistry• Petrology• Optics and Diffractometry• The list goes on and on …
BUT
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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.
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Geoscientists Should be Able Read, Understand, and Review the Popular
Literature
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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.
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What to Leave Out?
• Plutonic rocks
• Rock names• Texture names
Leaving this one out really sucks!
(Well, almost)
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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
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What to Include (2)
• Activity of silica• Activity of alumina
Mineral assemblages reflect activities.Activities can be related to chemistry.
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• 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
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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.
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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
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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.
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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
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Rock Names with Comfort and Support
Rhyoli
te
Andes
ite
Basalt
Where, in Rock Space, Does Comfort and Support Fall?
• Rhyolite
• Andesite
• Basalt
• Obsidian
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Explosive Eruptions, Craters, Calderas, andActivity of SiO2
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Quiet Eruptions, Lava Flows, and Activity of SiO2
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Organizational concepts come before facts.
Facts are learned by applying organizational concepts to case studies.
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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