An introduction to minerals and rocks under the microscope
An introduction to minerals and rocks under the microscope

This free course is available to start right now. Review the full course description and key learning outcomes and create an account and enrol if you want a free statement of participation.

Free course

An introduction to minerals and rocks under the microscope

2.5 Learning outcomes for Section 2

Now you have completed this section, you should be able to:

  • suggest different ways in which light passing through a crystalline material is modified
  • define the terms refractive index and birefringence
  • explain the meaning of the terms isotropic and anisotropic, permitted vibration direction, double refraction and pleochroism
  • describe how plane-polarised light passes through an anisotropic crystal on the stage of a polarising microscope
  • explain the origin of interference colours in anisotropic materials
  • describe how to identify an unknown mineral (in thin section) using a polarising microscope.

Now try the following questions to test your understanding of Section 2.

SAQ 4

A slice of an unknown mineral has been examined with a polarising microscope. In plane-polarised light the mineral appeared colourless, but when viewed between crossed polars it appeared dark, and remained dark as the mineral was rotated. To what crystal system is this mineral likely to belong?

SAQ 5

In plane-polarised light, a thin section of a mineral shows very high relief, but as the stage is rotated through 90°, this changes to very low relief. Why does the relief change with orientation? What prediction can you make about the interference colour for this mineral?

SAQ 6

In Section 1, you were introduced to the crystal structures of two polymorphs of carbon: diamond and graphite. Based on your knowledge of these structures, what prediction(s) can you make about the optical properties of diamond and graphite?

S276_1

Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has over 40 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to university level study, find out more about the types of qualifications we offer, including our entry level Access courses and Certificates.

Not ready for University study then browse over 900 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus