Quote Originally Posted by thebigspendur View Post
Emerald, aquamarine are all gem varieties of beryl. The stuff is massive and usually mined in Pegmatite Quarries. There are no xtls in the massive stuff like say a coticule
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If I had to make an educated guess from the picture
I would call this a "Chlorite rich quartzite". If it is, it
would hone a lot like a black Arkansas or perhaps a
translucent Arkansas hone. The green chlorite mica
may help keep the grain size of the quartz fine and
available as a cutting media.

I do hope someone with a lot of comparison hones gets to try
one of these. The differences between the possible mineral
compositions are large. However, that does not matter
when the proof is how good a hone it makes.

P.S: I do not think the green is kryptonite which would fog
old style film but who knows in this digital world