FMF - Friends of Minerals Forum, discussion and message board

[John S. White]

I am excited about introducing Forum visitors to what I believe is the most exciting work that has ever been done with optical mineralogy, or crystal optics. Dr. Olaf Medenbach, professor at Ruhr-Universitaet Bochum in Germany, has made optics his life's work and out of his dedicated efforts has come this instructional vehicle which makes understanding the complexities of optical crystallography easy to understand. Use this link to Olaf's Home Page, then look at Optical Crystallography (on the English version) or Downloads zur Kristalloptik (on the German one). Try out all of the various topics. Note that when you click on all except the first one, you will see a box open at the bottom of the page. Click on that and try out everything. You will find there the most wonderful windows into a world that few of us have ever visited. Unfortunately the last topic "Mineral Optics" is presently available only in German, and a couple of those above are in the process of being converted to English.

The link is: https://homepage.rub.de/Olaf.Medenbach

I would also like to point out that this is not a commercial effort. The work was done as an academic project for educational purposes only.

[mmauthner]

What a useful website! Thanks for passing that along, John.

Mark

[Ed Huskinson]

Thanks John, for this valuable link. My books on optical mineralogy are Kerr's 1959 edition on Optical Mineralogy and Bloss's 1961 edition of Optical Crystallography. So it is exciting to re-acquint myself with the subject. Olaf's photographs, both thin section and miniature, are breath-taking alone.

I rooted around through the site, enjoying myself immensely, grateful for the background I received as an undergraduate (Thank you Dr. Asquith!). It has been years since I've seen an interference figure. (I like the use of them as background for the home page). I even went to the Mineral Optics menu, and checked things out. Wish I spoke German, as the translation for this section is unfinished.

Again, thanks John, for the heads up on this valuable link. And many thank-you's to Olaf for authoring such a significant and useful contribution to the fields of mineralogy and optical crystallography. This site is a keeper, and has been placed on my favorites page.

[Gail]

Oh I can see that I might be spending many hours on this site, what an amazingly informative one it is too! I think some of the easy excercises using the computer screen might be a wonderful thing for our 8 year old grandson to experiment with. I love when there are things we can do together.

So, excuse me while I go "play" with optical mineralogy. Thanks ever so much for sending this our way John!
Well done!

[renpagan]

A wonderful website indeed. I hope it will be fully translated into English, so more people can use it, beyond enjoying the beautiful pictures and some of the best power point slides I have ever seen in any field.
I would not expect this website to draw a lot of frequent users, as it is very technical and quite above the level of most mineral collectors, especially those that are turned on only by wonderful aquamarine crystal groups, tourmalines etc. Anyhow I think it is very good to offer to the collectors the possibility to learn more about mineralogy and related sciences: in due time more people will be captured and helped to grow.
The Mineralogical Record published some issues that were very technical (on goniometers, microscopes etc.). Some readers were irritated as they missed their bimonthly fix of aquamarines and tourmalines, but I see that these back issues continue to be sold, as more people find about them and get interested.
So, Olaf, congratulations and ... keep up the good work!

Renato

[Jordi Fabre]

Renato, saluti e benvenuto qui!

I'm so excited to read Renato here.... Renato is a wonderful man and his knowledge about minerals and mineralogy is enormous, and, as we can see, his English language is exquisit.

I hope you enjoy this Forum and eventually publish here some of your mineralogical experiences. If you do it, many (or all) visitors of FMF will be happy. ;-)

Jordi

[Peter Megaw]

35 years too late! I could have really used these incredible graphics back when I taught optical mineralogy to unsuspecting undergrads. I might not change everything I did, like making them construct their own biaxial indicatrices, but they would have gotten a whole lot more out of it! I am delighted to see that mineral collectors with limited background in this subject are instantly capitivated by Olaf's presentation...and recognize that the inherent beauty in minerals viewed at this level can be systematically related to their fundamental crystallography. I always relished the responses the first time a lab full of students looking at thin sections of a dunite (olivine-rich mantle rock for the uninitiated) crossed the nicols/polarizer!

It is a shame that so many universities have ditched petrography...and the understanding of optics that underlies it. Various kinds of probes, X-rays, phase diagrams and Raman spectroscopy will never replace the information on interrelationships between mineral grains, strain history, and alteration that the trained eye gleans instantly from a thin section..and at minimal cost. I appreciate the arguments made for the modern "black-box" approaches, but in many cases the inherently high local variability of the earth renders modeling mineral, or mineral-fluid reactions, as interactions between a limited number of components indicative at best. Indicative is a good start, but these black-box approaches gain substantial weight if based on a solid foundation of field and petrographic observations...in many cases this "weight" is the difference between significant and meaningless results. Unfortunately, the training to perform these simple basics is being lost at all levels in Earth Sciences....so kudos to you if, like Olaf, you are one of the few who remain committed to training geoscientists in these noble pursuits.

The upside for those who care is that there are some real bargains out there for used transmitted light microscopes and there are still a number of labs that will make you a thin section of whatever you send them for under $20. Add a basic petrology book to Olaf's petrograhy presentations, and find out what that "granite" countertop in your kitchen is really all about! (And find out what a travesty it is to call it granite!)