This rock from Manicotagan has numerous veins of asbestos and also these peculiar green veins. The green mineral can be scratched with a steel nail. The rock has been described as serpentinite.
The white patch on one specimen is porcelain glaze for writing the name of the rock.
It could be volkonskoite ( Cr-bearing clay mineral of the montmorillonite - saponite group). The conchoidal fractures speak in favor of it. Normally the mineral color shows a more olive-green tint than this bluish one (?). There are other "minerals" like chloropal (nontronite variety) which I prefer second in the row.
H.G.Dill
Thank you Harald G. Dill for the identification.
My students have been trying to tell me that it was jade, but the hardness test failed them. Yes, it is very green, somehow the picture came out a bit bluish and it has conchoidal fracture.
Maybe we have a new chromium mine?
Thank you so much!
It could also be nephrite, a rock comprising mostly massive microcrystalline to cryptocrystalline felted amphiboles of the tremolite - actinolite series, and/or a mixture of species of the chlorite-group and the tremolite-actinolite series.
Nephrite-jade is softer than jadeite-jade and can be scratched with a steel nail.
X-ray diffraction analysis will help to identify.
Best regards,
Guenter Grundmann
Dear Dr. Issigonis,
please find inclosed another Cr-bearing variety which comes close to yours.
It is Cr-bearing illite in a fault zone cutting through granites in the Bavarian Forest. The Cr content is 8.69 wt. % Cr2 O3 . From the outward appearance it may resemble your specimen but it occurs in a K-enriched lithological system whereas yours - ultrabasic- is deficient in K. Therefore, I suspect a variety of the smectite group rather than the mica group. The conchoidal fracturing has disappeared in Cr illite infavor of a more platy one.
H.G.Dill
Thank you Guenter Grundmann for making me aware of the nephrite minerals. The color is definitely similar, so an XFD will sort it out.
I wonder why people gave the name "kidney-stone" to this (nephrite) mineral. I doubt if it is the color, probably the usual lumpy appearance of nephrite?
Your help Harald G. Dill is very much appreciated. Thank you for your keen observations and wide knowledge that makes your contribution valuable to all geologists.
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