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PhotosLarge augite from Kibo?? Must be anorthoclase

29th Dec 2019 13:33 UTCTony Peterson Expert

The photo of "augite" from Mt Kibo is surely anorthoclase with a skin of black glass; you can see the grey feldspar in nicks through the skin. A simple weighing would decide the matter, as pyroxenes are much denser. 
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1st Jan 2020 17:36 UTCUwe Kolitsch Manager

Message sent.

8th Jan 2020 19:33 UTCFernando Gascon Cuello Expert

I have studied the sample in more detail. In fact, its specific gravitie is 2.57 (in a scale +/- 0,01 gr), very different from that of the augite (S.G. 3.19-3.56). Inside the mineral is colorless, with abundant scoriaceous inclusions, both internally and externally, which gives it a blackish hue. I have not been able to analyze the refractive index, I have a gemological refractometer, but the sample does not have any plane adequate enough for the measurement. I think that you have reason, it is an anorthoclase, but and I think that, due to its specific weight it could rather be sanidine, the extreme term of the anorthoclase series: sanidine (S.G. 2.56-2.62) - albite (S.G. 2.60-2.65). Do you think I should calificate the sample as sanidine or anorthoclase ?. By the moment I have calified as anorthoclase because the literature dont reports any sanidine, but anorthoclase yes.

8th Jan 2020 20:10 UTCFrank K. Mazdab Manager

you could label it "alkali feldspar" and cover both sanidine and anorthoclase
 
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