Pencil "plumbago" (Latin for "lead ore"). Because the pencil core is still referred to as "lead", or a "lead", many people have the misconception that the graphite in the pencil is lead, and the black core of pencils is still referred to as "lead", even though it never contained the element lead. The words for pencil in German ("bleistift"), Irish ("peann luaidhe"), Arabic (قلم رصاص "qalam raṣāṣ"), and some other languages literally mean "lead pen". The value of graphite would soon be realised to be enormous, mainly because it could be used to line the moulds for cannonballs; the mines were
Lead natural rock sample depends greatly on the presence of these three parent uranium and thorium isotopes. For example, the relative abundance of lead-208 can range from 52% in normal samples to 90% in thorium ores; for this reason, the standard atomic weight of lead is given to only one decimal place. As time passes, the ratio of lead-206 and lead-207 to lead-204 increases, since the former two are supplemented by radioactive decay of heavier elements while the latter is not; this allows for lead–lead dating. As uranium decays into lead, their relative amounts change; this is the basis for uranium–lead