Quote Originally Posted by Howard View Post
You are enjoying a rare pleasure Chris and I am pleased for you. I have a collection of vintage coticules as well as other stones and it's amazing to reach back into the past through a well used hone. The magnesium oxide lines probably aren't cracks so much as veins - big difference! I love "figure" on my stones and I have customers who regularly buy well figured coticules for their collection. It's ironic that today people often expect coticules to be a pure cream yellow and will complain about figure or veins. There is no difference relative to the honing outcome if a stone is figured or has MgO in it. Figure makes a stone more interesting.

I have seen the opalescent effect (pearlescent is a new word to me) and doubt it is MgO that is causing it. I would guess mica or some other similar sodium/potassium magnesium aluminosilicate which is what makes up many minerals including garnet and mica which are fairly common. MgO is just dead black with no refractive properties. I have a wonderful table made of red sandstone from Arizona with MgO dendrites on it. I bought it from the hotel at Pagosa Springs where they were using it as a stepping stone at the bottom of a set of stairs. Yikes!
Pearlescent. If it sounds made up......it probably is! It sounds good though, doesn't it?

Thanks for commenting on this stone, Howard. Your opinion means a lot to me.

I received word recently from someone at the Ardennes mine in Belgium that prior to and around the year 1900, actual cracks in the surface of coticules were filled with a mixture of beeswax and glue of some kind. "The color of this filler was white to dark yellow/brown.".

Interesting stuff!

Chris L