More hardness than quartz -- help id

[tavernier]

The rock in the photography has a cloudy outer layer of approximately 3 - 5 mm of thickness; where that layer has been removed appears with an intense brightness metallic silver colour ( see closeup), its hardness is greater than the quartz. What rock could be?

 

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[Jonnybobrich]

Its just smoky quartz i would say

 

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[tavernier]

Hello Jonnybobrich:
I do not discard that; but that do not fits it is the fact that this stone is covered with an external layer of the same material, it is to say that it is "coated" , probably with "boart" crystal.
I do not find examples of coated quartz.
In addition to me the crystal shape resembles a distorted cube (to see first and second photography) that does not fit either with quartz.

 

[tavernier]

Hello:
When I wrote "boart" "coated stone" I was talking about this : ( The second image comes from : http://www.diamondrough.com/rough/r05a_pages/r5a_08.html )