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Is this gypsum?

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https://www.flickr.com/photos/128269620@N04/shares/w41Q64

https://flic.kr/p/u9189h Appears broken or sheared .

Very soft, easily scratched with fingernail. Composed of very thin sheets, some small pieces have flaked off, but not any large sheets. Also highly transparent, the orange staining on one side can be seen clearly through the good face.

From my great-grandfathers collection - I was told most came from Colorado, especially the Grand County area. Gypsum, CO is a couple hours away. He also brought some stuff home from Arizona.

Edit: Added photo.
asked Jun 7, 2015 by HappyDigger (220 points)
edited Jun 10, 2015 by HappyDigger

1 Answer

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Certainly looks it it could be gypsum, especially based on the described cleavage and low hardness. Are you able to stick a knife into it?
answered Jun 9, 2015 by hershel (46,480 points)
selected Jun 15, 2015 by HappyDigger
It is soft enough to stick the knife point through the sheets and the blade goes in easily parallel to the sheets.
In that case its almost certainly gypsum. Gypsum is sectile which means a knife can be inserted into its sheet-like layers.

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