Iron is by mass the most common element on Earth, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust. Pure iron is relatively soft, but is unobtainable by smelting. The material is significantly hardened and strengthened by impurities, in particular carbon, from the smelting process. A certain proportion of carbon (between 0.002% and 2.1%) produces steel, which may be up to 1000 times harder than pure iron.
Synthetic stones are created artificially in a factory or laboratory, but have the same physical, chemical and optical characteristics as their natural counterparts. These stones usually have high luster, and is difficult to tell the difference from natural stones with the naked eye.