Graphite is a mineral with a very simple composition — C & x28;carbon& x29;.  A sample from the Skaland mine in Norway which was once the leading graphite mine in Europe. Width of sample 10 cm. Everyone is familiar with this mineral because pencil “leads” are made of it. It’s named “lead” because centuries ago people thought that this mineral is a form of lead. Real lead have never been used to make pencils. Early pencils were indeed made of a stick of pure graphite but such mineral deposits are very scarce. The best source at the beginning of the 19th century was in England. These deposits were unavailable to the French because of naval blockade during the Napoleonic Wars. So they had to start thinking and very soon one clever man discovered that you can use impure graphite powder & x28;which is quite plentiful& x29; to make pencil leads if you mix it with various amounts of clay and burn the rods in a kiln. The hardness of the lead depends on the amount of clay & x28;more clay adds hardness& x29;.

圖片編號： 120118336
拍攝者： Sarfrazalii