Misc: In the abbreviation P & O, what does the O stand for?

Questions

What is the name given to the setting of gems into stone for example on the marble walls of the Taj Mahal?

Which voilet blue variety of quartz was used by the ancient greeks for making cups and goblets because it was regarded as a charm against inebriety?

GENERAL KNOWLEDGE; Which piece of opaque variety of quartz found in most parts of Scotland was set into the gold and silver baton that commemorated the 1986 Commonwealth Games in Edinburgh?

Imperial Units were phased out in England in 1999, which seven Imperial Units were authorised for retention as specialist terms?

In a perfect Brilliant stone, how many facets are there?