Spyderco was in business in 1978 but mainly sold the ceramic crock stick style sharpeners at the time...
please keep in mind that this was 26-27 years ago so don't put to much credence in the Wasihta reference I could very well be misremembering that....
This stone definitely does not have the opaque look of the Translucent stones that I have seen, but then again it is 1" thick...
This is one of the things that I don't like about natural stones, the uncertainty of what you really have, once the label is gone... I guess that could also apply to a few of the man-made stones too..

Again thanks for any help on this