石 'stone' +
灰 'lime/ash' +
石 'stone' = 'lime-stone'. Drop the trailing
石 and you get
石灰 (shíhuī, 'lime/quicklime'), the processed product — limestone (
石灰石) is the rock you mine to make lime (
石灰). The famous karst peaks of Guilin and Yangshuo are sculpted from exactly this rock.
