From Hand Lens to Microscope

Let’s start out by following the path of light in the microscope from its source to your eye, and then consider why the petrographic microscope is unique. Light shines upward from a light source in the base of the microscope and encounters a polarizing filter, a thin section of rock or meteorite, an objective lens, another polarizing filter, and finally the eyepiece (also called the ocular lens). Note the polarizing filters (also called Polaroids or Polaroid filters). They are an essential feature of the petrographic microscope. They can be rotated to completely block light passing through them, a position called crossed polars, abbreviated XP. If a thin section of rock is placed between them, most minerals glow brightly in beautiful full colors called interference colors. Another important feature is a stage or platform that rotates allowing you to analyze changes in crystal colors, brightness, faces, cleavages, and effects of impact shock. (Many other important tools and concepts used in petrographic microscopy such as conoscopic viewing, use of the Bertrand lens, and accessory plates are not covered in this field guide.)

The petrographic microscope is a highly technical instrument. To fully understand and appreciate its capabilities requires considerably more knowledge than we present here. However, newcomers to the petrographic microscope will find this chapter a great help in examining meteorites.