This is called the "hollow" cabochon.
"The Chemistry, Properties and Tests of Precious Stones"
John Mastin
This is called the "double" cabochon.
"The Chemistry, Properties and Tests of Precious Stones"
John Mastin
But on clear days, unfortunately rare, the blue sky was Mediterranean, and at such times the bergs out at sea would flash like jewels in the full blaze of the sunshine, while blocks of dark green ice, half buried in snow under shadow of the cliffs, would appear for all the world like cabochon emeralds dropped into a mass of whipped cream.
"From Paris to New York by Land"
Harry de Windt