The following is a short discussion of fluid inclusions in sphalerite that was held during July 1997

Hello to all !

I am trying to study fluid inclusions in sphalerite on my Reynolds' stage. Wafers are so thin that sphalerite appears to be light orange. However I observe that all cavities appear to be dark grey or black, which prevent me from seeing anything inside. Only in six or seven FIs, probably flat, can I distinguish something inside.

Has anyone an idea for observing FIs in sphalerite ?

Michel Dubois


Universite des Sciences et Technologies de Lille
U.F.R. des Sciences de la Terre - SN5
Sedimentologie et Geodynamique
Tel : (33) 03 20 43 65 47
Fax : (33) 03 20 43 49 10
E-mail :

Michel and others:

Many years ago when I was working at the U.S. Geological Survey we had the same problem. The reason that the inclusions appear dark is because the light is reflecting off of internal crystal faces in the inclusion (and not because the inclusions are filled with vapor).

The solution was to remove the sub-stage condenser unit and replace it with a fiber optic light source. The light guide could be adjusted so that the angle of the light path could be varied relative to the sample plane. By adjusting the optic path while watching a fluid inclusion, you can determine the correct angle to permit observation of the interior of the inclusion. Obviously, the optics will not be as good as if you were using a sub-stage condenser, but they are usually good enough for microthermometry if the inclusions are large enough.

Hope this helps.

Bob Bodnar


Dr. Robert J. Bodnar
C.C. Garvin Professor of Geochemistry
Director, Fluids Research Laboratory
Virginia Tech
Blacksburg, VA 24061
Tel: (540) 231-7455 (O)
(540) 953-2448 (H)
Fax: (540) 231-3386


I suggest you use strongly convergent lighting, from an appropriate substage condenser (see Fig 6.1 in my book). Also, sometimes the use of a fiber optic light source, from above the stage, may totally reflect off a facet on the bottom of the inclusion and up into the mike, giving you a good view of an inclusion that appears totally black with transmitted light. (See other kinks in Chapt. 6 of book.) An effective, but awkward, device to achieve strongly convergent lighting was illustrated in my paper in Econ. Geol . v.57, 1962, p.1045. One problem you might have also -- if your slides are too thin, perhaps all the inclusions are opened to the air and hence black?

Ed Roedder <>