Homework Exercises

Exercise 5. Mineral Formulas

This exercise is due on Oct 31, 2014.

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Learn how to convert a chemical analysis of a mineral, which is a weight-percent measure of composition, to a mineral formula. The mineral formula is a molar basis of the composition.

Probe Lab 2

The electron probe microanalyzer in the Department of Earth and Planetary Sciences. This instrument is capable of analysis of mineral samples as small as 10 µm in diameter.

You have to use a spreadsheet program to calculate the formulas. If you write the numbers down and use a calculator to get the formula, you’ll make mistakes. Almost certainly.

Exercise 4. Simple Phase Diagram

This exercise is due on Oct 15, 2014.

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Phase diagrams are commonly and widely used to depict the stability of minerals. Rocks can be though of as chemical systems. The state of the system, that is, the amount and compostions of the minerals in the rock, is “mapped" on a diagram showing temperature, pressure, composition, and any other environmental variables that affect the state. Here is the simple but important example of plagioclase.

Phases in the two-component system albite–anorthite at 1 atm. The phase diagram was originally determined in 1913 from experiments conducted by N. L. Bowen

Be sure to learn about tie-lines and the lever rule!

Exercise 3. Solid Solution

This exercise is due on Oct 8, 2014.

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Explore aspects of solid solution. The carbonate minerals are our example minerals. You will use the limits of solid solution to determine the temperature of formation of a metamorphic rock.

Brumado Dolomite

Dolomite with tourmaline from Brumado, Minas Gerais, Brazil

Many minerals are solid solutions of two or more end members. The compositions of minerals are potent petrogenetic indicators of source and conditions of formation of rocks.

Exercise 2. Symmetry

The second exercise is due on Sep 15, 2014.

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The second exercise a few aspects of symmetry in patterns. Our patterns are composed of atoms in crystals. This is a two-dimensional analog.

A simple two-dimensional crystal with two atoms arranged in in a p4mm pattern

Patterns in three dimensions, real crystal structures, offer more possibilities, but the principles of identification of symmetry content are well illustrated by this simple example.

Exercise 1. Atoms and Bonding

Here is your first exercise. It is due on Aug 29, 2014.

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Your first exercise is all about atomic structure and bonding. Actually, it’s all in the electrons.

Crocoite from Tasmania
From the Halpern Mineral Collection, San Francisco

The electronic structure of the bonded atoms is responsible for the macroscopic properties of minerals, including, in many cases, color.

Geology 310 © Theodore C. Labotka 2014