It is generally formed from molten material. Diamonds... certainly conceivable, but extremely difficult, because any oxygen present would burn them up at the needed temperature. However, valuable stones will melt in general, but at temperatures considerably higher than 1000 C. (2000 F). Quartz and other silicates tend to lose their strength at high temperatures, so they are not suitable for use as gemstones in themselves. Gemstones that are found in the ground can melt if enough heat is applied to them. This is usually done with an acid, which eats away at the rock's molecules, making room for more of the precious stone to show through. The hotter the acid, the faster it will work. So heating the acid before using it is important! Also important is keeping the gemstone completely dry when melting it down; otherwise, it will go cloudy from humidity content. Some metals can be used as gemstones by being heated to a very high temperature and then cooled slowly. These include platinum, gold, and silver. But most gems are made from minerals that are found in the earth's crust. They are always mixed together in varying amounts of different crystals. No matter what part of the world they are found in, gems are always beautiful.