Raman Microscope
Raman Applications
Index Measurement
Metamorphic Rocks
Plutonic Rocks
Volcanic Rocks
Sedimentary Rocks
Stereo Pictures





This page presents some examples of convergent light figures (conoscopic images) obtained with the petrographic microscope. The pictures were photographed with a phase contrast telescope inserted between the photo tube of the microscope and a bellow accessory attached to a digital camera.  The phase contrast telescope has the same function as a Bertrand lens but it is generally much less expensive.

In the first two group of pages, a non mathematical explanation of the features that can be observed in the conoscopic figures is developed with the help of diagrams and pictures. 



Conoscopy of Uniaxial Minerals.

 Illustration and practical explanations of images structures. ( February 2004).

1. Introduction.

2. Images in monochromatic light. 

3. Use of wave plate.

4. Use of quarter wave, Benford plate and quartz Wedge.

5. Conoscopy of crystals cut parallel to optic axis.



Conoscopy of biaxial minerals.

( February - March 2004 )

1. Introduction.

2. Figures perpendicular to the acute bisectrix.

3. Figures normal to one optic axis.

4. Accessory plates: 1l  and 1/4 l   plates.

5. Use of quartz wedge.




Animation of a conoscopic picture of a muscovite crystal cut along the cleavage plan ( perpendicular to the acute bisectrix). Click for movie.  Observe that isogyres are counter rotating around the poles of the optic axes.   



Beryl (Aqua Marine) normal to the optic axis. Beryl is sometimes pseudo biaxial.

Oblique section in Beryl.


Biotite, pseudo uniaxial.


Images of quartz nearly perpendicular to the optical axis


Topaz plate cut nearly perpendicular to acute bisectrix.

Random section of gypsum.


Feldpath nearly perpendicular to one optical axis.



Optic dispersion in chloritoid.