Granton Material Hardness

[Ptychodus04]

Does anyone know the Moh's Scale hardness for the shale/slate from the Granton Quarry? I have a prep that is going to require abrasive for the whole thing. The matrix just laughs at soda, so I'm on the hunt.

[Malcolmt]

Shale in general is a 3 on the scale with limestone being just a little bit harder. 

[Ptychodus04]

19 minutes ago, Malcolmt said:

Shale in general is a 3 on the scale with limestone being just a little bit harder. 

 

This Granton stuff is almost slate if not a true slate. Way harder than your typical shale

I'm thinking I need aluminum oxide but don't want to go that hard if I don't have to

[jpc]

dolomite or iron shavings....

[Malcolmt]

I have used 800 mesh silicon carbide mixed with dolomite . I never use aluminum oxide

[Jeffrey P]

The shale at Granton Quarry varies a lot. The bedding is tilted and capped with basalt. Shale that has been exposed to the elements tends to be "soft" flaky and tends to break up into tiny shards when you attempt to split it. The less exposed pieces (which tend to be bigger and more likely to contain complete fossils) are also much harder- more like slate. Sometimes you're lucky when you split a piece and the fossil is exposed on the seam. However, very often a thin film of very hard shale covers the specimen which as you know can be excruciating to remove. Out of about twenty plus feet of rock face only about an inch wide band has supplied practically all of the fish fossil specimens. Just extracting sizable pieces of shale from this very thin layer is itself a big challenge. I hope this information helps.

[Ptychodus04]

Thanks @Malcolmt, @jpc, @Jeffrey P

 

Yes, this is the super hard stuff. One fish, I believe I can scribe off the matrix as the fish is bigger so I can see it better.

 

I'll start with the dolomite and silicon carbide as suggested. Going to take a piece to my geologist friend to get a good hardness test done just so I know.

[Malcolmt]

The ratio I use is about 20% silicon carbide to 80% dolomite. 

[RJB]

Good luck Kris.  Sounds like a tuff job this one.

 

RB

[Ptychodus04]

4 minutes ago, RJB said:

Good luck Kris.  Sounds like a tuff job this one.

 

RB

 

This one makes my eyes cross!!