Another mineral for this A-Z, quartz on a Moroccan stamp sent just in the last few weeks (and saving me from going with Q is for Queen ;) .
Don't be fooled, this stamp is tiny (slightly smaller than a Royal Mail Machin definitive). It was issued last year in a set of 10 'Roches du Maroc'. I couldn't find a nice image of the set unfortunately.
Sent on this lovely postcard from Eva.
For more Q subjects on postage head over to explore the links at Sunday Stamps.