In hand samples, I observe some of the blue stains in the serpentinites, so what is this mineral?
Dear Mr. Masoud,
there are two groups of asbestos found also in some serpentinites. The white asbestos is made up of serpentine-group minerals normally poor in Fe and the blue asbestos is composed of fibrous amphibole often enriched in Fe. It is actinolite and crocidolite. Locally, colorful mineral aggregates such as Cat’s-eyes of sub-gem quality may occur.
Another type is described as follows. Silicification of riebeckite is called tiger’s-eye or an equivalent gemstones as hawk’s-eye owing to its bluish tint. Quartz containing oriented fibers of crocidolite or riebeckite displays a special luster. Tiger’s eye is displaying chatoyancy (a vertical luminescent band like that of a cat's eye). It is in parts a function of the Fe contents and the special intergrowth of the phyllosilicates involved in the alteration process.
Best regards
H.G.Dill
Thank you, Prof.Herald, but I made XRD and thin sections and these minerals which you mentioned are not found.....I think that it is a type of serpentine mineral, that is right?
Dear Mr. Masoud,
in this case I can only suspect of having coloration due to the type of intergrowth which I mentioned above. Which minerals did you indentify by XRD ?
H.G.Dill
antigorite, chrysotile, lizardite, carbonate, iron, and clinochlore but in very little amount
In general, the Mg-Fe-bearing chlorites are green but I know some of them which show a bluish or bluish green tint. Apart from the intergrowth I have no explanation for this mineral assemblage others than chlorite to be accountable for this bluish tint.
Regards
H.G.Dill
I have found that very fine, dispersed magnetite can give a bluish cast to veins in serpentine. I'm not sure why this as magnetite is opaque. Maybe dispersion around the magnetite grains.
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