Titanium
Titanium, with the atomic symbol Ti, is a relatively new metal in jewelry use. First employed for industrial and commercial use, its applications range from military hardware to replacement for bones and cartilage in the human body. Extraordinarily strong (almost as strong as steel, but 50% lighter), it also withstands corrosion and is an inert metal. It is also hypoallergenic, making it the ideal metal for those whose skin is sensitive to alloys found in gold and silver. Titanium pieces are very durable and extremely strong, allowing them to withstand years upon years of use. They are also exceptionally comfortable and lightweight. Titanium is also forged with a high level of purity (nearly 100%), unlike gold and platinum.
Titanium is classified in four "commercially pure grades," ranging from 1 to 4, level 4 being the hardest. The majority of titanium jewelry being marketed is made from aircraft grade titanium, which is titanium alloyed with aluminum, vanadium and tin. This mixture of titanium is the hardest there is and it should be noted that this specific titanium alloy is very difficult to cut, refinish and engrave.