FMF - Friends of Minerals Forum, discussion and message board

[Robson Vieira]

Hi everyone. Dueling about to distinguish a sample between topaz and euclase I have faced with the question of the cleavage of each one, and with the highly technical subject of Miller indices of cleavage planes. Euclase has the clinopinacoid (101) perfect cleavage direction as the topaz has the basal (001), if I'm not wrong. I would like to ask you all to explain in practical terms what I need to know about cleavage planes and Miller indices to help me to identify crystals. I have the basic experience with different types of cleavage, but I would like to be confident with the numbers of the literature. Is it really needed to study crystallography? Anyone know a practical guide?
Thanks
Robson

[Bob Carnein]

Whether it's necessary to learn about crystallography depends on how serious you are about adding to your identification skills and whether you care about the "whys" of many mineral properties. Crystallography is a great help for those who want to develop some level of independence, in which they don't have to constantly rely on others for help. It also allows a collector to communicate clearly with those who already have such skills. No one has to know crystallography in order to collect minerals, but that knowledge also helps you to evaluate specimens that are offered to you for sale or trade.

Learning Miller indices and the fundamentals of crystallography are not easy tasks for the beginner. The best way to learn is to look for a class or course in which you can obtain "hands-on" experience, working with models and then with natural crystals. Being able to ask questions and get clear answers and to work with friends who are also struggling with this is far better than trying to wade through by yourself. You may find, also, that a light introduction is not very satisfactory--you need to immerse yourself in the subject for a period of time. I recommend a college class, if you can find one. If you are an independent learner, I recommend trying a text such as an old edition of Dana's Manual of Mineralogy, which does a good job introducing the basics. However, interpreting pictures in a book or on a website won't provide you with the knowledge you can obtain from a hands-on class.

[lluis]

Hi

Euclase is known because it can mimic practically all.
I would suggest asking for an analysis.
Hardness of topaz is higher than euclase (8 to 7.5), but the density of euclase is lower than topaz (2.99-3.1 versus 3.4-3.6) ... If you can measure such....

With best wishes

Lluís

[Jordi Fabre]

[Josele]

I tried to explain how Miller indices work here:
https://www.foro-minerales.com/forum/viewtopic.php?p=151654#151654 (in Spanish).
Maybe this can help...