It has the colour of one, it is as hard, but it has a mixed sort of structure I haven't seen before, with inclusions more like certain Arkansas stones - your expertise gentlemen, if you please!

Overall size: 126 x 55mm

Dry:
Name: Charnley dry.jpg Views: 1166 Size: 27.7 KB

Wet:
Name: Charnley wet.jpg Views: 1161 Size: 30.7 KB


Full size scans here and here.