Introduction

    PetroGlyph© is an interactive computer program designed to help Earth Science students learn to identify minerals in thin sections of rocks and classify thin sections according to rock type. The program is essentially a "virtual" microscope that simulates the major features of optical and electron microscopes. Optical microscope views include: plane polarized light, cross-polarized light, reflected light and Bertrand lens views. Electron microscope data are available, including a cathode luminescence image, seven element maps, a backscattered electron image , and energy dispersive X-ray spectra. This version of Petroglyph contains thirty thin sections of igneous, metamorphic, and sedimentary rocks.

    This manual includes an overview of a petrographic microscope and a guide to using PetroGlyph. It provides instructions and an overview of the images, functions, and tools available in PetroGlyph and how to use them. Words in bold type in the hyperlinked glossary.

    Our the latest information about PetroGlyph, visit our webpage at http://www.geology.byu.edu/petroglyph/.

A brief introduction to a petrographic microscope may be useful in understanding PetroGlyph.

Ocular (or eyepiece)- magnifying lenses through which the thin section is viewed.

Bertrand lens- a lens which is used to observe interference figures, in conjunction with the auxiliary condensor.

Objective lens- the primary magnification lens in the microscope. Most microscopes are equipped with several; magnifications range from 2.5 to about 40X.

Stage- the surface on which the thin section sits. The stage can be rotated to observe properties such as pleochroism and extinction.

Goniometer- a ring marked with angular increments (0-360 degrees) used to measure degrees of rotation of the stage.

Lower polar- the lower of two polarizing films; used to filter out light that does not vibrate in a plane parallel to the polar.

Light source- generally an incandescent light source is in the base of the microscope.

Upper polar- the upper of the two polarizing films which can be removed for viewing thin sections under plane polarized light or inserted for viewing under cross-polarized light. It is oriented perpendicular to the lower polar.

Accessory plate- an opening is provided for the insertion of one of several accessory plates. The most commonly used accessory plate is the gypsum plate.

Auxiliary condenser- an extra condensing lens that focuses the light on the back of the objective. It is used in conjunction with the Bertrand lens in order to view interference figures.

Condenser lens- focuses the light on the area in the sample that is immediately beneath the objective.

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